Connectivity is absolutely shocking.

I totally agree. What a duplicitous arrogance for Sonos to make a wi fi speaker that will invariably have serious connectivity issues and blame their poorly designed speakers on the buyers router/ modem. I just put my Sonos Play: 5 in the garbage can. I will not further annoy myself by describing the Kafkaesque experience of how my Sonos Play: 5 after working fine for years on the same Xfinity modem/router stopped connecting and the ensuing stultifying  time consuming crushing banalities of time wasted. I feel much better now. I will never buy another Sonos product nor of course would I recommend Sonos to anyone. I just ordered a highly recommended bluetooth speaker.

1000%.  I as well have had multiple Sonos products for years, running in 2 households on Xfinity routers without any issues until about maybe 6 months ago. Since then all the issues listed here; app (both S1 and S2) very frequently not being able to connect to the speakers, occasionally not even seeing the system. 
 

it’s maddening when all you want to do is listen to music. 
 

I’m going to try the assigned IP address solution (if that can even be done on the xFi router). 

Update 

So I finally gave in and got a router, Archer AX 55, and put the Xfinity modem into bridge mode.

Not a single problem since, running both S1 and S2 systems concurrently.  This also fixed AirPlay connectivity issues, and the issues playing directly from the Spotify app to a Sonos device.

And the good news is relatively inexpensive at about $90 on Amazon, and ridiculously simple.  Not being an IT person I was not sure if, by using same wireless network name and password, all pre-existing devices would automatically attach to the new network, or whether I would have to spend a whole bunch of time reconnecting the mall.  Happily they all automatically connected.

I did try ‘reserving’ IP addresses in the Xfinity app, which is as close as you can come to assigning a static IP address, but this didn’t solve the issues, just slightly decreased the frequency.

Not sure if this whole issue is a Sonos hardware / software deficiency, or something to do with Xfinity’s hardware, but I’m just glad the problem is solved.

Hopefully this fix helps someone else out there.

The original thread was started before the new Sonos S2 app was released 7 May but I suspect you had issues with the latest app as well(?).

If you have free time to check things it would be interesting to know what differences the new AX55 router and the Xfinity have in their default settings - if any. I’m thinking that is it some setting (other than the bridge mode) that now makes the system work better or is it just the new router’s overall performance compared to the Xfinity?!
 

Issue predated the new (and crappy UI) S2 app released recently; was hoping that would have magically fixed things but clearly didn’t.
 

per the much more expert posts above and in other threads, it seems to be with how Xfinity router handles DHCP. 

to be clear, I didn’t need to assign static IPs w/ the new router.  Just works as it should.

Reserving IP addresses is the suspenders part of the ‘belt and suspenders’ rule. If the router is behaving properly, it shouldn’t be necessary. It only helps when the router itself gets in an ‘odd’ state. 
 

Well, and being good housekeeping for a network, but strictly, if everything is working properly, it isn’t completely necessary. 

You are not the only one. We have spent thousands of dollars on Sonos equipment and probably 20-30 hours in just the last 6months on hold with Sonos, trying to fix our problems, and researching on my own. I have never once heard from Sonos I had a router problem. This is insane that I could spend this kind of money and NOBODY with Sonos told me I needed an additional router? I’m a legally blind person and the effort it’s taken to just get music playing is absurd. I’m researching getting different music system. I would NEVER recommend Sonos. Soo disappointed. 

E-mail received today from Audioengine with subject “When Your Home Audio System Turns Against You: Broken Apps”. Points to lengthy marketing piece contrasting “the allure of a sleek, proprietary system” with “open compatibility and user freedom”. (Spoiler: They think open beats allure.) “SONOS” doesn’t appear even once, but they do point to the Wired article reporting on the May update debacle.

I fully sympathise here and find that Sonos equipment is utterly useless at connecting, whether wifi or AirDrop. I have actually given up and switching out to Bose. I have experienced nothing but problems with all of my Sonos speakers, literally every time I use one of the speakers there is drop outs, cannot find the speakers or god knows how many updates are needed for speakers. I have just come to use them now and my Ipad or MacBook cannot find the Sonos Play 5 that is next to me. All Sonos ever say is it’s my network that is the problem in one way or another, you’re meant to be a network specialist to get these working every time. I have had new routers, new Ipad, new phone, new laptops and even tried in a different house and all just experience nothing but trouble. I have Bose speakers and never have any issues, I have a cheap soundbar from a company called Majority and that works fine, but Sonos is just endless issues to the point I spend more time trying to fix the problems than actually using it so there is only one place for such bad equipment and that is the bin! How Sonos can actually sell these products when they are so poor then claim the issues are due to wifi or network is beyond me. Google is plagued with people having so many problems and yet they are never fixed.