I had this issue before and I gave up on the product but after a few months, replugged it in and it worked fine. 

My sound system had been working fine for many months and I got the Sonos Sub which I loved but now randomly this issue has appeared again.

Sonos beam keeps flashing a white light even though I have it connected via ethernet cable to the router. I’ve tried unplugging the router as well as the Beam. I can’t even factory reset the beam (doesn’t matter how long I hold on to the join/infinity button, it keeps flashing white). Very frustrating as I got the subs + 2x SL ones to pair and now none of them can connect to my TV.

Diagnostic number: 197347082