Hi leeaoniao,
Thanks for providing a video and the FLA!
The issue you are experiencing is related to Layer Parenting.
There are lots of bugs in Animate's Layer Parenting implementation, so its use should be kept to a minimum, only when necessary.
Do not have it on all of the time.
Unparent your layers, using Layer Parenting Toggle to switch parenting off.
After you remove the Layer Parenting, snap the feet back into position to fix your existing keyframes, using Smart Magnet Joint [ ` ].
Only when you finish your animation, enable Layer Parenting where you need it to generate arcs.
Please, read this article to get a good idea when and how to use Layer Parenting in your SMR workflow: https://flash-powertools.com/smr-and-layer-parenting/