Rig not exporting into blender properly

I’m currently trying to export a viewmodel rig from Roblox into Blender.
The rig:

When I import the rig into blender using a plugin from this post and attempt to rebuild the rig, it rebuilds the rig of the gun and humanoid root part but not the arms. No errors.
Image of the rig in blender

What is causing this?

Note: I rigged in rig edit lite