Finally working for me.
I first deleted the v2.db and restarted HA but that didn’t work or at least was not sufficient.
Then the day after I coincidentally figured out that after I completely shutdown the HA (Settings > System > Hardware > press three dots > shutdown Hardware), unplug power cable and back in after some seconds to trigger the HA to boot up again. Now I had to login again and the new add-ons were all working.
The difference with the regular reboot is that I had to login again which was not the for a reboot as it then goes automatically to the main page of HA.
Before deleting the v2.db I think it’s worth to first try the shutdown procedure above as I don’t know exactly what was the trigger to have it working. Maybe a simple log out/in is already sufficient!