I would also try a reboot of your router, but after that, I would suggest  that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, there are more options available beyond just the diagnostic analysis. 

After spreading the word about how great iBroadcast is all over this Community, I am now having this exact same issue.  I have a Galaxy S8 and am using the S1 controller.  Tried removing and re-adding iBrodcast music service, but that didn’t work.  I really do not want to reset my router, as currently all my other connected devices are working just fine.  I sent an email to iBroadcast hoping to hear back - they seem to have much more accessible customer service than Sonos.

PS-I can’t browse my iBroadcast library using the Sonos controller on my PC, either, so the issue is not only with Android.

May be worth trying a reboot of your router, while you wait to hear back. I’d follow that up by a power cycle of your Sonos devices, just in case. 
 

Of course, my previous suggestion stands. 

Thanks, but a reboot wasn’t necessary.  The developer wrote back and said he was aware of the issue and was actively working on it with Sonos.  A few hours later he confirmed that the issue had been resolved.  I checked the Sonos app, and all of my iBroadcast tunes were there!  Yay, I still love iBroadcast!!!

Wow that is some great support. Better than Google have ever provided to the many suffering YouTube Music customers, for example.