Uninstall the app, then reinstall it. Reconnect to your system. That usually fixes the issue.

I have this problem when I connect my ace headphones to the app. It works as long as I keep the app open but once I close it I have this problem when it crashes as soon as you open it. I have to clear the storage data which is in effect the same as reinstalling. It then works fine until I add the headphones back. If I don't add the headphones it stays stable so I just add the headphones periodically to check for firmware updates and then just go through the clearing the data down process to get the app working again. It really is time they had the app sorted by now, it has been months, total incompetence. This Spence guy should be fired for what he has done to the company.

I’ve now removed the app from my iPhone, but in the AppStore I only get the option to open Sonos and crashes instantly 

Weird. Try Search your phone for the Sonos app maybe it’s still installed. 

@User971197 

Are you using an iOS or Android device and what is the latest OS version on that device?

Says they are using an iPhone in their post. 

The app was still present in the App Library, managed to delete and reinstall, all working for now. Thanks All!