Is the difference defined by whether the model is a $staticprop?

This is normally to do with the presence or absence of animations. For legacy reasons all SMD meshes are rotated 90 degrees from their final engine position, as your tarpaulin model shows, and that error is then corrected by their animations rotating them back.

No, but you can download the latest code from GitHub if you need the changes now.

Damn, this bug is two years old! It will be fixed in the next release. Only SMD imports containing vertices with the same position but different weight maps were affected.

The names will always be truncated, there is no way for an add-on to avoid that.

Names are only generated for corrective shape keys, which I don't believe are ever referenced in a QC file.

I've pushed some changes to the repo[github.com] which fix this problem. The exporter will now derive a corrective shape key's name from its animation drivers, if there are any.

The importer will now automatically generate drivers for corrective shape keys. To generate them for an existing import, use the button in the Flex Properties sub-panel. And of course you can edit them yourself through the normal Blender UI.

Tell me if this works for you.

This was a case of the up axis transform being applied twice, and it will be fixed for the next release.

But please note that after the bug fix your animation "ragdoll" is still rotated 90 degrees from vertical - that's in the data being imported.

I'm not going to fix this: it's an edge case, merging objects can break other DMX features, and renaming the shape keys would still be destructive.

You have two options to avoid the problem. Either merge the objects yourself, or rename the shape keys and use advanced flex mode to generate a flex controller which targets both at the same time.

I didn't see the error you mentioned when exporting Collection 1, but I did see this:

Warning: 220 verts on "broke's css" have over 3 weight links. Source does not support this!

That would explain why the animations look different.

I'm having a hard time unpicking the arrangement of objects in the file. There are some meshes that I can't make visible in the 3D view, even though they are visible and their collection is enabled.

The error message and the line number don't match, which suggests that the scripts didn't load correctly. Restarting Blender might fix this.