I'm curious as to what people consider to be the most problematic subclasses or class features.  I'm also interested to a lesser extent on other issues such as itemization problems (lack of official items to boost unarmed monk attacks for example) or spell issues (perhaps spells that should be on a list but are not or spells that you think are useless).  

Please keep this discussion focused on what you think is problematic.  Please avoid disagreeing with each other.  I'm not necessarily interested in who is right or wrong.  I'm more interested in player perceptions.  I also want to keep it focused and not have it devolve into a debate.  If you'd like to share any solutions you've come up with I'd be happy to read those as well.

I really liked most of the optional class features in Tasha's.  I generally think they were great and solved some issues with some classes and subclasses.  I am curious what things people would like to see addressed next.

Well, I think that the Paladins Divine Senses and Ranger's Primeval Awareness are both so watered down in terms of effect that they're basically useless.

At the risk of turning the thread into another Ranger debate, I'd throw Favored Enemy/Favored Terrain in there with Divine sense and Primeval Awareness.

Problematic = diverting the campaign from where I was planning to take it so that these situational features aren't totally or mostly useless. A lot of people are okay with building their adventures around this stuff and I do that sometimes as well, but sometimes you already have an idea of what you want to do and it's annoying to have to shoehorn in some giants or goblins or whatever. But if you don't you're not really allowing the class to work as intended. 

I don't know if it's a relevant answer to this thread... but the biggest problem with classes features in 5e is that martial classes are set on a linear progression path with no choice and no customization options beyond feats... The few subclasses which do add options are usually have that choice be their only subclasses feature... In my group, our rogue will get increasingly frustrated with his linear progression as the casters of our party will get to pick and chose every level.. with every second level unlocking new and fun options... Martial classes are simply much too simple and boring in this respect.

SLightly more on-topic I have a problem with subclass specific features which don't work well with core class features.

The sun soul's Radiant Sun Bolt not working with the martial arts extra attack or stunning strike for example. Anyone taking the subclass probably wants to be a ranged monk, but you are discouraged from committing to that role... I feel like the monk generally suffers from the interesting subclasses not actually being stronger than the monk's base options because the subclass features are so restrictive and sometimes straight up weak.

The eldrich knight is also a strange subclass for me... They gain the ability to make a bonus attack after casting a cantrip/spell, but this feature becomes gradually weaker as you get more of the fighter's signature many attacks. It would have made a lot more sense if the ability worked similar to the updated bladesinger. The subclass also to only two spell schools, one of them being evocation, probably the last school any non full caster would want to have access to.

Also, sublcasses that are so front loaded that WoTC have crippled their higher level features seem really disapointing to play in a long campaign... The rune knight gets all this cool stuff at early levels but get basically nothing interesting at later levels... Your level 10 feature is going frmo 1d6 to 1d8 extra damage per turn... an almost meaningless increase... Imagine working your way to level 10 for that.

Hmmm... most problematic class feature.  Well, people talk about sorcerers and rangers having bad features, so lets not get into them.  The rest... aren't really class features, but just general issues, I guess, that kind of relate to a lot of classes.

To me, short-rest dependent classes (warlock, bard, monk, etc) are kind of screwed over at times, because short rests aren't consistent. Relatedly, once-per-day spell warlock invocations are dumb - for some reason the devs thought being able to cast Bane or Slow repeatedly would be too powerful, while Hypnotic Pattern, Fireball, Counterspell and Fly aren't an issue.

Multi-classing in general I consider problematic, simply because my experience has it boiling down to one of two results - vastly inferior or vastly superior than a regular class, and I'm not great with wildly different power levels. I hate how I have to deal with players that don't like me saying no to multiclassing. 

I haven't tried any of Tasha's new summons or Beastmaster pet... but I have serious problems with the original Conjure spells, Animate Dead and the chain pact/beastmaster/paladin mount. Or cohorts/sidekicks/whatever you call them. 

Poisons suck for PCs. Actually, this is pretty true for most "evil-aligned PC stuff" - dealing with fiends/undead, etc. This makes it harder to play a more villainous-themed character, like an assassin or evil cleric, compared to something more heroic. 

Two weapon fighting is badly implemented this edition. 

Most problematic? Honestly, high level magic. There's plenty of annoyances here and there among specific class features, sure, but nothing is problematic like balancing campaigns around 8th-9th level spells.