The issue, in short: Every class table - i.e. the thing that lists what features you get at which levels, as well as things like spell progression (where applicable) or the progression of other relevant class abilities (barbarian's number of rages/rage damage, monk's damage die/ki points/Unarmored Movement, rogue's Sneak Attack damage) - has links from each class feature name to the description that appears later in the page.

However, for many of these tables, at least one or two features have links that don't work. When I check the page's source code, it turns out that the section link in the table doesn't match the page anchor in the source code attached to the feature's heading. Often, this problem seems to occur when there's a feature with a number of uses or bonuses that grows over time, and the number of uses is noted in parentheses next to the feature name at each instance of improvement in the table; in these cases, either the link in the class features table is missing the parenthetical that appears in the anchor link in the source code, or vice versa. (Most other times there's such a problem, it's also related to issues with punctuation, such as the presence or absence of hyphens or apostrophes.)

Coinciding with this problem, some classes have scaling features that repeat the description (with a corresponding section heading) each time the feature improves (e.g. the Barbarian's Brutal Critical), while others simply provide the feature description once and link back to that each time the feature improves (e.g. the Bard's Bardic Inspiration and Song of Rest).

• Barbarians: The class feature "Brutal Critical" adds a single extra damage die on a critical hit (in addition to the already-doubled damage dice) at 9th level; this increases to 2 extra dice at level 13, and 3 dice at level 17. However, in the Barbarian Table, for each mention of the feature, only the words "Brutal Critical" are linked, pointing to the nonexistent #BrutalCritical page anchor. In fact, in the class features themselves, the feature is listed 3 times - once for "Brutal Critical (1 die)", another for 2 dice, and once more for 3 dice. The actual page anchors are #BrutalCritical(1die), #BrutalCritical(2dice), and #BrutalCritical(3dice). (In the book, the actual "Brutal Critical" description only appears once, as with all scaling features.)
• Bards: This one's actually a pretty simple error, no parentheses involved. The 3rd-level feature is correctly listed as "Bard College" on the table, with the link pointing to the anchor #BardCollege - but the feature is incorrectly titled above its description as "Bardic College", with the corresponding page anchor #BardicCollege. I say "incorrectly" because the physical PHB labels the feature "Bard College" in both the table and above the feature description. (Also, note that the Bard's Bardic Inspiration and Song of Rest scale, but each mention in the table only links the words "Bardic Inspiration" or "Song of Rest" to the single time that the description of each feature appears below - unlike the barbarian. This matches how the 2 features are listed in the book.)
• Clerics: No problems with section links! Again, the number of uses of Channel Divinity and the CR for Destroy Undead scale, but each feature description only appears once, and each mention in the table simply links the feature name (not the parenthetical) to the single time each feature description appears. "Divine Intervention" also improves at level 20, and similarly the text "Divine Intervention Improvement" links back to the "Divine Intervention" feature description. (Minor note: "Improvement" is capitalized in that feature's name in the Cleric Table on D&D Beyond, but it's lowercase as "improvement" in the table in the book. Actually, this is also true of subclass features for every class - e.g. it says "Divine Domain feature" in the Cleric Table in the PHB/SRD/basic rules PDF, but D&D Beyond capitalizes "Feature" in the Cleric Table.)
• Druids: Again, no problems with links. As with clerics, "Wild Shape Improvement" links to the main "Wild Shape" feature description. (And again, it's lowercase as "Wild Shape improvement" in the physical book.)
• Fighters: Similar problems to Barbarians, but slightly weirder and more inconsistent. The weirdest: Extra Attack. The first "Extra Attack" is listed at level 5 in the table, "Extra Attack (2)" at level 11, and "Extra Attack (3)" at level 20. In all 3 cases, only the "Extra Attack" text (not the parenthetical) is linked, pointing to the page anchor #ExtraAttack. However, if you actually look at the feature descriptions below, the feature is actually listed all three times (with the number of attacks changed in the description each time to fit) - but it has the same heading of "Extra Attack" all 3 times. And if you look at the page source, each of the 3 times it appears, it also has an identical page anchor of #ExtraAttack. Naturally, if a page anchor is attached to multiple sections of the page, the browser just points you to the first time it appears in the page if you click such a link. (In contrast, the Action Surge and Indomitable features also gain more uses per rest as you level up, but each of those features only appears once under the feature descriptions - and where they're listed in the Fighter Table, only the text before the parenthetical is linked to that single instance of the feature description.)
• Monks: "Ki-Empowered Strikes" is listed in the Monk Table at level 6, pointing to the page anchor #KiEmpoweredStrikes. In fact, the heading above the feature description actually has the page anchor #Ki-EmpoweredStrikes, including the hyphen. (As with similar scaling features for clerics and druids, "Unarmored Movement Improvement" links to the single "Unarmored Movement" description, and as in those cases, "improvement" is lowercase in the corresponding class table in the book.)
• Paladins: No link problems. As with other classes' corresponding features, "Aura Improvements" and "Sacred Oath Features" are capitalized in D&D Beyond's Paladin Table, but "improvements" and "features" are lowercase in the Paladin Table in the physical PHB. (Also, "Aura Improvements" actually links to the Aura of Protection feature description, which makes sense as there's no separate entry for the simultaneous improvements to the radius of both auras in the actual PHB.)
• Rangers: Another punctuation-based link problem. The "Land's Stride" feature is listed at level 8 in the Ranger Table, pointing to the page anchor #LandsStride (no apostrophe); however, the heading above the feature description has the anchor #Land’sStride. It may alternately display as #Land%E2%80%99sStride, as the punctuation used is actually not a regular apostrophe per Unicode standards but actually a "right single quotation mark"; if you replace the character with a regular typed apostrophe, it won't jump to that section of the page. Also, each time the Ranger gains another Favored Enemy, the entire feature description - including the full list of creature types (and their descriptions, which don't appear anywhere in the PHB, apparently taken instead from the intro to the Monster Manual) - is repeated; each instance has the identical page anchor #FavoredEnemy. In contrast, the Natural Explorer feature description only appears once. (Each time a Favored Enemy or Natural Explorer improvement is mentioned in the Ranger Table, it points to the same pair of page anchors - and obviously, the Favored Enemy link always takes the reader to the first instance of the page anchor.)
• Rogues: As with Rangers, there's another apostrophe-based link issue; the 1st-level "Thieves' Cant" entry in the Rogue table links to the anchor #ThievesCant, but the actual feature description has the page anchor #Thieves’Cant (or #Thieves%E2%80%99Cant - again, it's a "right single quotation mark" instead of an actual apostrophe). In addition, Expertise is correctly listed at both 1st and 6th level in the table, as rogues get expertise in 2 skills at 1st level and 2 more skills at 6th level. However, as with fighters, the feature description is repeated once for each time it appears (unlike the PHB, where the description only appears once total), and again, both listings have the identical header of #Expertise, so the browser just takes you to the 1st instance of that anchor in the page.
• Sorcerers: No link issues. "Metamagic" is accurately listed in the Sorcerer Table at each level when the caster gains more Metamagic options, but each instance correctly links to the single description of the feature.
• Warlock: Similar to Barbarians, there's an issue here with parentheticals and repeated feature descriptions. "Mystic Arcanum (6th level)" is listed at warlock level 11, "Mystic Arcanum (7th level)" at warlock level 13, "Mystic Arcanum (8th level)" at level 15, and "Mystic Arcanum (9th level)" at level 17 - but each time, only the words "Mystic Arcanum" are linked, pointing to the nonexistent page anchor #MysticArcanum. In the feature descriptions below, however, each instance of the Mystic Arcanum feature appears separately (a total of four times), with the page anchors #MysticArcanum(6thlevel), #MysticArcanum(7thlevel), #MysticArcanum(8thlevel), and #MysticArcanum(9thlevel) respectively. (As with other such features, the "Mystic Arcanum" feature description only actually appears once in the book, with the additional Mystic Arcana at higher levels simply detailed in the one feature description.)
• Wizards: No link issues here. (There are barely any features to the base class besides ASIs, so there's not much to get wrong.)

And just for good measure, let's include Matt Mercer's homebrew Blood Hunter class, which has a special listing on D&D Beyond thanks to his/Critical Role's partnership with the site:

• Right away, the 1st-level Hunter's Bane feature predictably has the same linking issue with apostrophes as other such features; the entry in the Blood Hunter Table points to the nonexistent anchor #HuntersBane. Uniquely, though, this time the correct page anchor (#Hunter'sBane) actually uses a regular apostrophe; if you simply type an apostrophe there in the URL, it will take you to the right section of the page.
• Also, for most classes (e.g. rogue or ranger), the "[Subclass] Feature" entry in the class table points to the top of the list of subclasses (e.g. #RoguishArchetypes or #SacredOaths), instead of the early-level feature that lets them choose the subclass (e.g. #RoguishArchetype or #SacredOath); the "Order Feature" entries in the Blood Hunter Table buck this trend by linking to the class feature each time (#BloodHunterOrder) instead of the top of the list (#BloodHunterOrders).

I've also pointed out some other (unrelated) issues with the Blood Hunter in a separate post.

A summary:

• Some classes have broken links in the class feature table, pointing to nonexistent anchors. Sometimes this is due to punctuation differing between the page anchor linked in the table and the actual page anchor associated with the corresponding feature description, whether that's due to parentheses (e.g. the Barbarian's Brutal Critical) or apostrophes (e.g. the rogue's Thieves' Cant) or even hyphens (e.g. the Monk's Ki-Empowered Strikes).
• Sometimes the linking issues are also due to the unnecessary repetition of class feature descriptions, with the multiple improvements of the feature listed separately but with an identical page anchor (e.g. the Fighter's Extra Attack).
• ...And in one case, it's just because the feature description has the wrong heading (the Bard's Bard College feature is incorrectly titled "Bardic College").
• In general, there's inconsistency between classes (and sometimes within classes) regarding whether a feature that improves/gets more uses at higher levels has its description repeated (e.g. the Ranger's Favored Enemy) or not (e.g. the Ranger's Natural Explorer).
• And finally, a minor issue: all listings of subclass features, and some "improvements" to existing features, have "feature" or "improvement" lowercase in the PHB class tables. It may be worth changing the D&D Beyond capitalization of these features in the class tables to match, to make it clear that it's a reference to the existing feature and not meant to be a "new" feature.

Please fix the broken links, and make things more consistent about the repetition. Personally, I'd suggestion getting rid of the repeated entries for scaling features, and match the PHB's formatting for those entries - have a single entry for such a feature, and link back to the same one when there's an improvement at higher levels.

(There are similar linking issues with the monster lists in the Table of Contents for the Monster Manual - and possibly some of the other monster books such as Volo's and Mordenkainen's - but that's a task for another day.)

Quote from filcat >>

Barbarian done. It might take a while, but I'll get those done.

 Thanks as always! <3