First thing to check:
Press left ctrl + i to open Node Constraints -> Look for anything referring to nip or bust
(Example scene made by Unica, card by Kyonko)
If it isn't that:
Open up Timeline -> Check for the same
If this was the cause, you might have to go into KKPE -> Unfold Modified -> Select any Bust bones that have been changed -> reset pos/rot/scale
(Example scene by Giddora. Example card by Pis)
If it isn't any of that:
Search Dynamic Bone Collider in the Workspace, see if any of them are overlapping the tits and either move them or delete them.