Hmm, it seems to be exactly what I said: duplicated faces/vertex.
I had a similar issue in the past, but I don’t know any better method than simply deleting these duplicated vertexes and faces and caping the holes. I’m not sure but it might mess up with the UV somehow so keep an eye on it.
Whenever you are unable to cap a hole it’s probably due another duplicated vertex/face you have around that hole. It seems your mesh is full of messed up face and vertex duplicates. Do you still have the source of this model ? Have you checked if there’s a version of this model that is clean with no duplicated vertex/faces ?
Weird that fbx isnt working. Anyway, I don’t know how experienced you are in modelling but the best solution I have is to get the clean model to export as OBJ, or any other format that won’t cause these duplicated vertexes and faces, then redo the rig (maybe use Skin Wrap, since I use 3ds max). I’d rather redo the rig than fix the messed up mesh and possibly UVs, but that’s just me, there might be other ways to fix you problem but these I posted are the ones I know and the ones I’d try.
Also, no problem, sir, I help whenever I can, hope you’ll find some way around this problem, because right now these suggestions are all I have, sadly.
It depends on what game/program it is and what you’re using to compile the model(s), but it varies since there’s no definite limit that’s actually listed (at least as far as I’ve looked into and read up on; there’s supposedly a limit of 65536 indexed vertices, but I’m pretty sure people have passed that over several times in the past). There’s also some .QC functions that can help you get around those limitations by making use of multiple $model entries in the .QC before compiling.