One of my players can't see the fireball spell on their staff of the magi anymore, it also doesn't show up in their spell list from the staff. Their normal fireball spell is just fine, so I assume the problem is with the staff? All other spells on the staff seem to be fine, and removing/readding the staff didn't fix it either.

Does it show up in their 7th-level spells? It's meant to be cast at that level.

It does not.

Are they using a homebrew version because it works 100% perfect for me and and always has.

Nope, it's the original. If it were homebrew I'd have tinkered with it to try to find out why. Fireball just randomly disappeared sometime in the last 3 weeks where we weren't playing. It still shows up for one of my npcs, so I'm not sure what's happened with this character in particular. It was there, then it wasn't.

can you post a link to the character sheet, please?

What happens if you try to "wake up" the character, by clicking the Inspiration box twice and then reloading the page, to refresh the data cache?

https://www.dndbeyond.com/profile/xirestra/characters/33514796 , Tried the wake up, no luck :/

Yeah, Fireball is gone from it. That's definitely a glitch of some sort.

Or maybe it's a weird interaction with the homebrew Draconic Sorcerer? Or the Necklace of Fireballs? What happens if you unequip the Necklace?

I've done some testing and it is a bad interaction with the Necklace of Fireballs, presumably because they both create a Fireball spell entry that uses charges.  If you have both on you then the Staff gets overriden.

EDIT: I also checked the Wand of Fireballs and the Wand of Lightning Bolts with similar results, so it appears that any spell that uses charges from an item creates a conflict.

The subclass hasn't conflicted with the staff the entire past couple of months the player's had the staff. As for the necklace, I've unequipped it and the fireball from the staff still doesn't show.

The necklace might need to be removed, not just unequipped.

Edit: I can kind-of confirm that the Necklace and Staff conflict with each other, but in my test the Necklace is missing the Fireball spell, not the Staff. (I added the Necklace after the Staff.)

Edit2: Also, reload the page after removing the item.

 Your solution worked Naruhoodie, thanks. Just gonna refund them the gold cost of the necklace. Thanks for stickin' with me on this!

Happened with me too, only it was a Staff of Power and Necklace of Fireballs. Your solution worked, naruhoodie. Thanks!

Had this same problem with one of my players characters, except they originally had the staff of power and upgraded to the staff of the magi later on, so unattuned from power and attuned to magi but both Fireball and Lightning Bolt were missing. It wasn’t until I read this and completely removed the staff of power from their inventory that the spells appeared in their list!

Thanks!