@animation Import Issue

I've imported a large variety of animations into Unity to work with and all have functioned correctly without issue. I've been running into a problem recently though where if I rename an animation in the mesh@animation format Unity seems to break the import and one of the bones is being ignored.

It looks like this:

When importing under a regular animation.fbx name it works fine. As soon as it's changed to mesh@animation it breaks as mentioned. Very odd. I'm not a modeler and this was done by someone else. Would anyone be kind enough to shed some light on this situation?

Thanks!