strange datapack interaction in 1.21.10 from 1.21.8

so i've been working on a custom food datapack. i got it to work in 1.21.8, but still needed to add a geyser-safe method of eating so i hadn't expanded on it too much yet.
in 1.21.10, the code that worked before is strange now. i didn't do anything to the old code except to update a scoreboard name and change the food item properties.
what it's supposed to do is:

detect if a player is holding a player head using a fake uuid reserved for a food item (1003000,1003000,1003000,1003000, sweetberry pie). only ones that don't have nbt yet. i found this only worked if i specified an empty name in the check.
clear exactly 1 of only the nbtless heads.
replace it with 1 of the food nbt heads, now it looks and behaves like food.
recurse the function so it only fires if the player is still holding more nbtless heads.

when testing the new geyser eating function, i had to make sure the new properties worked first. but then i ran into a weird problem.
first, it wasn't detecting the heads anymore. i had to take out the empty name field to make it work again.
second, it does a really weird thing. when i receive an empty head with the fake uuid, it starts oscillating between a player head and the custom food model.
third, when i get it to stop doing that, it gives me two of the item now instead of one.
it's not a SUPER big problem because i only put this in as a failsafe kind of thing, to make sure the proper foods were being spawned and so i could be lazy and just be "uhh give player head with uuid" and it'd still have all the nbt. so my pack isn't broken by heads duplicating.
but i want to know why it's doing that. it didn't do that in 1.21.8. it's only doing that in 1.21.10. it seems like a lot of things changed in 1.21.10 and it's not documented anywhere?
attached:
the chocolate cake function is from the 1.21.8 pack.
the sweetberry pie function is updated for 1.21.10, and is duplicating heads when given a blank head with the right uuid.
the recursive check.