Try unplugging the Beam from power for a couple of minutes and reboot your router.

Hey Thanks, I tried all that the last weeks. Updated router firmware as well. I also did a complete factory reset. Did not help.

I noticed this:  when I power off the Beam and restart the router, these 2 One SL’s are not connected anymore. even if I wait 5 minutes to give them a change to reconnect.  I had to unplug them to get them back into the system.

I have to decide this week if I will bring the whole system back (30day money back warranty). I was always very suspicious about wireless speakers. Turns out I was right. 

Are you able to wire the Beam directly to the router with an ethernet cable?

I can do that for a test but I will install a new router first and check if the problem continuous. 

Today I noticed my subwoofer (mini) is having the same dropout problems. 

Sounds like a 5Ghz problem to me. In a Sonos surround set up the Sub and the surrounds are connected to the soundbar via a dedicated 5Ghz link. They are not directly connected to your router.

Ok thanks, I did not know that. The problem is getting worse.

• The audio level is constantly fluctuating. You almost get seasick. 
• Audio completely drops every 20 minutes. So multiple times in a movie. 

Did you speak to Sonos about your last diagnostics? If not, generate another and give them a call. That should help identify the problem so we can suggest a fix.