Please upload your .blend file.

It's an internal Blender error in a development build. Nothing to be done about it.

That's very cool! I probably wouldn't ship that with the tools directly as they don't deal with shaders or textures, but I would happily add a link to your addon to the website when it's read to ship.

What format version is the file in question?

It's the same process in both versions, only the icon has changed.

To be more specific, the model 22 format is used by Source 2.

Can you upload the DMX file that you imported? The importer will set the model format to 22 if it detects Source 2 features, and I assume that you didn't do it yourself. So there might be something strange about that model.

This is intentional. You can move the exported mesh by giving it a parent, such as an Empty object.

https://developer.valvesoftware.com/wiki/Blender_Source_Tools_Help#Meshes

Please upload the DMX files you are trying to compile. Unless they spoil anything about Half-Life: Alyx that is...

Morphs are applied on the GPU and are only supported with specific shaders. Try applying an existing face material and seeing if that fixes things.

All Source engine models have a skeleton/armature. Can you upload the files you are trying to import, please?