Hey. My issue here is a walking animation I made on a rigged humanoid in Blender that appeared to be working fine in Blender with all the clothing layers, but when I import it as an fbx or blend file in Unity there is a minor difference in how the animated rig affects the clothing in Unity. The only area affected is a little area around the knees as you can see.
I have done a few animations from Blender into Unity and not had this problem yet so I am at a bit of a loss as to what to do here.
At that keyframe the cloth simply moves underneath the character mesh. You just need to fine tune it. Try adjusting the allowed error in the import options.
I do have this working now but I’m not sure exactly how I did it. The thing that changed it was the Skinned Mesh Renderer Component, the quality on it needed to be set to 4. Other factors that I believe also influenced it was the Z axis direction of the bones on Blender as suggested and setting the animation compression off.
I think it just needed a bit of tinkering in a couple of areas but that’s what I’d take a look at if you are stuck!