@USBFIG Oh that's awesome! Ive learned neat stuff from your IG in the past. Thank you for sharing so much stuff, it's awesome when the Blender community shares knowledge openly. Definitely gonna check out your patreon later!
@LeNardoragon It can result in nightmare explosion stuff like that. I'd try removing shapekeys from the animation one by one around that part of the mesh and see if you can spot two competing keys.
@LeNardoragon Few possible things it could be. To me that immediately looks like conflicting blendshapes are active at the same time. If you have a hide fluff neck shapekey for example, and then another hide fluff shapekey that also includes the same parts of the mesh as that first shape key.
@KOTHUBPPL Drag and drop that on the avatar to set that animation as it's default state in your base animation layer temporarily (just remember to delete it when done or it will always pose you like that till overriden)
@KOTHUBPPL If you need to keep that FX layer, you can hit animate record to trigger the bicycle pose, go to the root object of your hierarchy, overrides on your inspector side, and reset the overrides for the armature or bones, and then save that as an animation clip.