What device are you using?  Have you tried the web interface? https://login.sonos.com/

Same problem - going round in circles, loging in multiple times (app and website), each time login seems to work, I can see my system and services in use - but the app keeps asking for System Manager login in a loop when I try to manage one of my devices. Where is the system manager set? I am the only user on the account.

I have tried to avoid using the app since the upgrade - I can see why people are so frustrated, its a complete disaster from a customer experience perspective.