After looking at the csv files and stuff, I think the issue has something to do with trying to create a new piece of equipment out of thin air. It appears to work fine on the player, but enemies don't take it the same way.
Edit: The problem are not the enemies, I tried giving Kaboom! to myself and using it, and the error was the exact same.
Edit2: I think I know what's going on, after reading the docs thoroughly, I realised that Kaboom and Fly Bite are the only 2 items in the entire game with the tag 'giveeqtarget', which according to the docs, replaces the bottom middle item with something else. Now, the issue is that more often than ever, the middle bottom slot is already occupied by another piece of equipment, and if I had to guess I'd say it doesn't delete the piece of equipment in that slot either, thus creating the error.
Edit3: Maybe it's just the fact that 'giveeqtarget' is the only script that destroys an instance, neither 'giveeq' or 'replaceeq' do this, and they still manage to normally replace the equiment that originated the new one.
Edit4: Yeah I created my own item using 'giveeqtarget' and the error was the same, it must be an error with that script.