I use maya, but I’ll try to throw in some things that could be the problem?
Make sure root is at 0,0,0?
Did you freeze transforms on your model before you bound it? Might have data messing it up
Could be a scale issue mesh could be to big/to small
Maybe a hierarchy issue?
Also it looks like you have technically 6 rigs? Doesnt look like all your bones are parented together which could mean roblox is trying to figure out how to interpret that? (might be a blender thing)