How exactly are you putting the spells into the feat? Did you add every single spell to the feat? If so I'm going to say you're overloading it doing it that way.

I think the best way for you to do this is create a feat for each class.

Bard Spells
Cleric Spells
Druid Spells
Sorcerer Spells
Wizard Spells

Under each feat add a spell and instead of adding the spell itself add the class under spell class and then at the bottom tick is infinite. This will allow you to pick a single spell then another dropdown will appear allowing you to pick another.

The problem I encountered is that I have ALL of the Spells from all 5 Classes, and unless I split it up into Multiple segments, I was stopped at the Bard's Eye Bite, which is nowhere near the last Bard Spell.

I currently have it split into 50 Spell entries in a single Feat that gives me 999 Domain Spells. The Feat is not the problem though, as it loads just fine, until I try to get into the Spells tab of my Character Sheet.

By the way, it took me 6 Hours to figure out how to do it thanks to the EXTREMELY confusing interface that the Homebrew Content Creator has, it's honestly a surprise that it is even half as popular as it is.

I can't even add extra Spell Slots because it requires an entry that has no available options and no Text Entry field, so if anyone wants to create such an effect, they simply cannot. I would like to blame IKEA, but they don't do Website Design.

This is actually the 3rd bug I've found today; try expanding the Legendary Flame related weaponry in the Add Equipment Menu of the Character Builder, you'll find the Quarterstaff types don't like to be expanded. Unlike that bug though, this one prevents access to my Spell Page, which was the entire point of the Feat adding up to 1,000 (Eye Bite isn't even #200, so there's another bug to look at)

Specifically I have each Level of each Class split into a different entry, and I am using the "Add Class, Restrict by Level" method specifically, I even told it to Cast as a Lv 20 Caster with the appropriate Stat, and they are all marked as infinite. I would love to mark them explicitly as prepared, known, and using Spell Slots, but I don't have that option unless I figure out how to recreate the Shadow Sorcerer Archetype, which is the only way to locate such a feature.

That is correct, we cannot add additional spell slots through feats. We can only do that currently by homebrewing the race you are using and adding spell slots that way. I have no idea what a legendary flame weapon is. It is your feat, but your feat doesn't produce anything on any pages except your spell page so your character sheet is fine until you click on your spell page. I feel like you're simply overloading the spell page. You're attempting to shove every single spell on the page.

I meant Very Rare, not Legendary. It had been a very long day, all of which I spent on DnD Beyond, building whatever I could with what limited tools I had. here is one of the 2 Weapons that is bugged when trying to look at them from within the Character Builder's Add Item Menu: https://www.dndbeyond.com/magic-items/staff-of-fire?comment=1

I am aware that I am adding every single spell (for Druid, Bard, Sorcerer, Wizard, & Cleric), that was literally the Wish, and the GM granted it. I just hope that the PDF is more agreeable, as it is capable of downloading, but I haven't yet opened it, as I still need to add the rest of the Spells (I have the Feat equipped to do it, and it is built properly, I just don't have it all selected yet on the Character side)

The whole point of this Bug report was the specific reporting of exactly this bug. I even went through the Sheet last night, and it works fine, until I click on Spells, exactly like we both said. My Wild Shapes are fine, despite containing every Beast, Monstrosity, Giant, & Fey. The Spells Page though is not capable of even briefly loading.

I unfortunately (or fortunately for me) cannot replicate any problems with the Staff of Fire. I have recently given my players a Staff of Fire and Staff of Frost. We haven't had any errors come from looking at them yet. Nor do I get an error when adding them through the character builder; even when I expand them.

On the note of the spells Stormknight bought up a good point to me. You know you have access to every spell. Why would you want literally several pages of spell names printed out? I'm obviously guessing here, but there's surely no way you're memorizing every single one of these spells. You're going to end up looking them up anyway to see what they do exactly, because the pdf doesn't provide a description of the spell. You know you have access to them so you might as well use the spell search function when you want to use that spell.

Obviously it came up as a bug and that's why you're reporting it. Makes sense. I just feel like in the long run if you're adding the spells so you don't have to refer to the internet to see your spells perhaps buying each class' spell cards from a game store would be a better idea.

I can't even afford food for the month that is why not buy something for it that lacks the capability to do Ctrl + F

Builder, NOT Sheet as your Screenshot shows.

They don't have infinite Spell Slots, simply the Knowledge of the Spells. I have 5 classes, using 3 Ability Score Modifiers, with up to 5 different ways to Cast some Spells.

If I wanted to do it myself, I'd use an Excell Spreadsheet.

You say it is the easiest way to do it, but I am a Shadow Origin Sorcerer.

Quote from Blue64 >>

You say it is the easiest way to do it, but I am a Shadow Origin Sorcerer.

 You just need to make a copy of the subclass and add the other class spell lists as Stormknight shows you. Then use the copy of the subclass and not the original.