After effects keeps changing keyframes on itself

I've been using after effects for a few years and I have never seen this happen before but it is happening, I gave a few lessons on the software for my girlfriend and all went fine but now after effects keeps deleting random keyframes and changing some , for example when we play around with position key frames everything goes well but as soon as we make keyframes for rotation , the ones we made before for scale are now completely different or nowhere to be seen as if they were deleted.

For context , we are trying to animate a body falling into water and we've separated its limbs and we are animating each one in its own layer , lets say we are done with the arms and want to start animating the legs , as soon as we are done with the legs , the arms get all funky and misplaced 

what am I doing wrong??? Can't find anyone with this problem anywhere