I upgraded last night and it was easy. The app asked for network, Bluetooth and location access. I allowed the first two, but denied location access.Why does Sonos need your location anyway?

It then asked me if I wanted to setup a new system or join an existing system. I selected join an existing system. It showed me a list of speakers on my old S1 system as well as the speakers on my S2 system. I selected the S2 system and it found everything. Granted, I do have 5 of my 11 speakers hardwired to my network. So that may have helped me with a seamless update.

After V80, I had all kinds of problems connecting to existing system.  Eventually, it found the system and connected.  I realize this isn’t a very tangible answer.

Something I've noticed with V80 is there seem to be a lot of timing problems.  When I launch app, it can’t find the system. Then finds it in a couple of minutes. When a track changes to the next song, the app shows the old album cover and title for a couple of minutes, then advances.

Try turning off the boost if you have one.