Ok, a few more tests.
Another computer, just installed SP1 and only 1 of 8 plugins got loaded.
In Civil 3D the plugins get loaded but not in AutoCAD.
As far as I understand the plugins are not loaded if the PackageContents.xml contains this
SeriesMin="R21.0" SeriesMax="R21.0"
If you remove this, the plugin will load but that is not a solution of course. I'll log this bug.