Perhaps more specifics might be helpful? Which radio stations on Sonos Radio are missing their artwork?

Greatest Hits Radio - there may be others.

Let’s see if someone else who is a Sonos Radio subscriber can check on their system. I, unfortunately, am not. That might help determine if it’s a local issue. 

I’ve chnaged its source from My Tuner to TuneIn, and the logo appeasr there …….Strange ???

I’d say so. I’d think both companies are pointing to the same server source…but I’d be guessing. But suggests it isn’t a Sonos issue per se, and not Sonos Radio, but an issue with myTuner.