I've just noticed, inthe logs, that a json file is not in the right place , here are the errors starting from line 5258:

[Render thread/WARN] [dev.kosmx.playerAnim.minecraftApi.PlayerAnimationRegistry/]: [WARNING FOR MOD DEVS] Animation player_animation/casting_animations.json is in wrong directory: "player_animation", please place it in "player_animations".

LatestLog Client

Steel here if you need more info/logs :)

It's pretty self explanatory
Just rename your player_animation folder to player_animations
Add an s to the end of the name

Where can I find it? I can't find a folder with this name in the modpack root or in the config folder, it doesn't appear when I search either

@MonkeyzMC are you a developer or a user?
If you're a user close this issue and report this to whoever made the mod with player animator as a library that's causes this issue
Looking at the name of the animation I assume it's some sort of spell mod?

Yes this is a spell mod, either Ars nouveau or Iron's Spell & Spellbook, I'm a user I can't find the name of the mod that causes this error, so I'm closing this post until I post it on the mod concerned