No help but I see the same thing.

Not sure but I may have stumbled on the reason for this. I'm running the Android app. When I last had the problem I had a look at what other apps were open in the background. When I closed them all, the Sonos recently played list reappeared. Can't remember if I had to close and reopen the Sonos app.

I've not been able to test this enough to be sure this is the issue, but will whenever I see the problem.

Maybe others can give this a go and see what happens.