previous case with suzanne was a mirror that works in a bad setup, this is a mirror that doesn’t work in a setup that is supposedly good (considering you auto-weighted it). try turning off “topology mirror”
here’s how all this shit works:
if you have an object that’s PERFECTLY symmetrical, both x mirror with and without topology mirror works
it may happens that you have tiny offsets between your righ and left vertices in space, in these cases, topology mirror will help you by identifying the topology and vertices connections do determine if a vertex is the opposite of another vertex. but in order for the topology mirror to work, your entire model needs to be perfectly topologically symmetrical you can have all the offsets you want in position, but not a single difference in connections and arrangement. if your model has both tiny offsets here and there, and a single vertex that is not connected like it’s opposite equivalent, you’re fucked. and you better come with a fresh mirror modifier before continuing. but you’ll lose your uvs :))))
and theses rigs on smutbase are broken.
Oh and by the way, if you ever come up to make your own rigged models from scratch someday.
you should definitely scale it by ten. It’s a lot better for a whole bunch of reasons. blender generally terribly manages small assets. and anyway a good rig is a scalable rig