If your Sonos devices were not powered down while you rebooted the router, it’s likely you have some duplicate IP addresses bouncing connections to the speakers. 

Nope - no dupe IP’s.

Gonna add to my list see if anyone has a clue here.

• iPhone app very slow. (on all phones)
• Its at least two songs behind what is displayed.
• Album artwork sometimes displays.
• Very often get the generic “cannot connect to server” message.
• Very often get the “cannot find media etc.” message
• volume control slow to respond.
• Similar issues at the controller UI  (response and control issues)

I am sure it’s the latest update as all was perfect prior to this.

Curious as to how you determined no dupe IP addresses, normally speaking it’s somewhat hard to see without very specific software.

All of your symptoms point in that direction, and since this issue isn’t appearing in thousands upon thousands of threads, it sure seems like a local issue, rather than something endemic to the update, which most folks are using without issue. 

Easy go into the ORBI router config UI and you get a list of attached devices by name, IP and mac address. (21 devices in my case. and i use the DHCP from the router.

and i am an ex-WiFi engineer :-)

It seems more like controller upgrade issues, but i may just shut the whole system down and let the devices come on line manually pain in the a$%)

As an  ex wifi engineer, just get a network trace of the UPnP calls between your controller and a player and see what is taking the time.

Maybe you could use iTunes or TunesKit iOS System Recovery to turn your iPhone back to normal.