in blender, enable Weight Link Cull Threshold. Re-export model.

Yeah, looks like smd error. Thanks for pointing.

I cannot import this particular smd into Blender.

Blender version: 2.79b
BleST version: 2.10.1

smd: https://drive.google.com/open?id=1pOj7C4DohOyT6OnSl7t9rgmYxz4E73Y5
traceback: https://postimg.org/image/aro863wdx/

Hmm, I'll try batch replace shape object in all bones with simple script then. Thanks for advice.

Try Noesis

How do i make smd_bone_vis object visible and selectable so I can edit it?

You could add SWEP.ViewModelFlip = true into your lua code so it is mirrored without messing with model.

Steam/steamapps/common/<Gamename>/bin/

A full compile log would be informative

qc script must include flex controllers defined inside

https://developer.valvesoftware.com/wiki/Flex_animation