How do I debug issues with the default animations for a new avatar?

Working on importing a humanoid avatar with additional bones (hair, tail). When the player walks in game, especially backward or diagonally, these bones move all over the place in absurd ways, despite their parents moving smoothly. The tail will spin around or stick out the front of the model.

How do I put the avatar into these walk cycles within Unity so that I can play them back slowly and figure out what’s up?

(Or, if anyone has some idea of why bones that don’t match up to any normal humanoid avatar trait do that sort of thing - what can I do about it? I think it’s something to do with the split bone hierarchy of the model I’m working off of.)

too many reason for it occurrence, show a video/gif?
show some picture of it armature?

Dynamic bone probably. Add collider to block them to go through your body.