In this example here, you can see that all the vertexes are messed up. However, in Blender, this is not the case. From testing around in Unity, it seems that (outside the Avatar Configuration page) the vertices are attached to the wrong bones in a specific but predictable order.
With my leg bones, I have 4 each: thigh, calf, foot, and toes respectively for each leg. The calf bone has the thigh vertices attached to them, the foot bone has calf vertices attached to them, the toe bone has foot vertices attached to them, and the toe vertices are left unassigned, making them attach to the origin instead of a specific bone.
With my tail bones, I have tail, as well as tail.001-tail.005. Tail.001’s bone has tail’s vertices, tail.002’s bone has tail.001’s vertices, repeat the process until you get to tail.005’s vertices, which as expected attach to the origin as they are unassigned.
I’m fairly sure that this is either a Unity issue or a Blender export issue, as the bones correctly have their vertices assigned in Blender itself as well as the Avatar Configuration page within Unity.
(Also to note, none of the other bones (such as fingers, ears, etc.) have this issue. They seem to be assigned correctly for whatever reason.)
By the way, upon reverting the fbx the issue is fixed, but I really don’t want to spend another 5 hours recreating the same fbx from the one that works.
Any help is appreciated!