Try rebooting your router and phone.
I took a look at your profile and saw how many devices you have, and it's a really nice system. I have 11 Sonos devices of varying ages in my system like you but I do not have any connection issues.
With the Play 5 in your system, I assume you are using both the S1 and S2 apps, just as I am doing.
Do you have any speakers/devices hardwired to your network? Are you able to remove the Boost and connect the Amp and Soundbars instead? Some users found that using the Boost caused connection issues, but removing it fixed it.
My suggestion would be to hardwire your soundbars and the Amp if possible. Do not wire a surround speaker or Sub if you cannot also hardwire the main speaker. While it may be inconvenient, you may want to give it a try to see if it helps.
Hi @Garryandco
Welcome to the Sonos Community!
Sorry to hear of the issues you’ve been having with rooms going missing from the app.
Long term occurrence of this issue is very likely due to duplicate IP addresses being handed out to multiple devices by the DHCP server built into your router.
To rectify this issue, I recommend reserving IP addresses for each of your Sonos devices in the router’s settings. How to do this changes with each router, but you can reference the manual if stuck, or if your router is supplied by your Internet Provider, they should be able to assist you. Reboot the router afterwards.
I hope this helps.