Blender 2.90.1
Blender Source Tools 3.1.0
Example model: https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=312134319

When decompiled with Crowbar 0.68, these 2 lines are in the "Outfit_Casual.smd" file at the end of the nodes section:
Changing to this allowed it to import (i.e. removing the the hash [#] characters):

I have confirmed that both the original and the recompiled model with the hash characters show up correctly in Garry's Mod model viewer, so the hash character seems to be a valid bone name character.