UPDATE 2:
I managed to “band aid” the problem.
on the Construction script on the children BP I manually set the anim class, location and rotation. this works somewhat, but if I do any movement related stuff like jump or crouch it resets the location of the player.
This should not happen, is should use all the references from the parent BP. and it only started doing this on 4.15, before that (since 4.7) I never had any issues with this. I also never changed anything related to animation of the character for a long time, so I am sure it was not something I did that changed something