Could be that as it tilts the HRP is knocked around causing the tilting, I wouldnt be sure how to fix that but try smoothing out the between frames to correct for the tilting by tilting the animation in the reverse
alright so by going through a video of the animation frame by frame, i found out that it was only tilting when i hadn’t keyed the lower torso during the animation. if i key the lower torso for every frame of the flip, it doesn’t do any wobbling or titling.
based on this, i’m assuming it had something to do with how the physics was handling the in-betweens? i’m still not sure what caused it, but at least there’s a fix!