Trouble with creating masks with images over a cartoon.

Hey everyone, hope you are all safe and well.

Okay, ill try my best to explain my problem. I am making a video of cut out images over an already existing cartoon. Like importing images, masking the faces out, then editing the motion, scale, position and rotation frame by frame to match the movement of the cartoon characters.

The edit has usually gone well but there has been a couple instances where I put an image onto the timeline and the scene im trying to edit kind of glitches and scatters, like the frames become sort of jumbled, when i take the image out the cartoon/video seems to run normal again but as soon as I put the image back on to editing the face frame by frame it is all out of whack.

Ill try and add a video to explain, 

cheers.