In the editor I can sort of preview transitioning from an animation to another by clicking the second one after the first is almost over, and said mesh does snap back into setup position for the transitioning time.
It does the same in Unity and in game. The coder tried setting 0 delay and 0 mix, so one animation would play right after the other and says it freezes.
The file is pretty big and complex, I'll record a video highlighting the problem to go along with it or it would be a mess to point it out. I'll do it with this mesh I discovered today and the other animation I mentioned. I keep finding weird behaviours tho, and this same file mostly worked correctly from 3.6 so I'm assuming something changed with the version switch
Thank you, I'll email you in a moment