About these weird faces connected together when using Load UV, I've seen it occurred several times, just create new UV channel in Rizom then the mesh'll display as good as normal, but the UV channel imported from FBX sometime make the mesh display very wrong.
The UV Channel imported from FBX :
Still that file, just create and switch to new UV channel in Rizom, the mesh displayed good now
It's not really the exact same problem as the original post here, because although the mesh diplay wrong, UV channel 1 still visible and can be export then imported back to Max successfully, that's acceptable for me now (also no warning about UV vetexes count inferior on import).
The chair in original post completely lost channel 1, which I think is a bigger problem.