@valerostudio
I also see this issue.
When you enable a plugin it might load as an extension but it is not active.
It does not appear under the extensions list, toolbars etc.
Sometimes it works, but others it fails.
After a restart it changes as you'd expect.
Something has changed in the API that's preventing this being consistent.
Most odd...
I am looking at the causes and a fix...
It's almost like SketchUp now prevent you from activating just some extensions/plugins on the fly...