"Adding music to library" in loop - error checking update ROCK

So now I’m getting the “There was an error checking for an update” message too, regarding ROCK.
Roon version 1.7, build 667. The OS is version 1.0 build 227.
Perhaps related to this: I added 142 music files and the software is endlessly trying to identify them, wthout result.
Of course I recycled the soft- and hardware by rebooting via the Web GUI and powercycling the i7NUC. I even recycled the switch the NUC is behind.
And I checked the networking settings - NUC IP adress, Gateway and DNS Server settings. They all are as they were and functioned perfectly for > 2 years.
But no joy. So hm.

Did you try reinstalling the os from the configure Rock system status webpage?

Thanks for your suggestion. Reinstalling the OS had no effect…

I might add I checked port forwarding for the ROCK device, both UDP and TCP, and ports 9003 resp. 9100-9200 are forwarded.
Still no joy. So I guess this is a question for Support.

Could a mod please prune and graft this to the Support part of the forum, or do I post it again?