Turn the Play 3 and the router off at the wall, and close the Sonos app.

Turn on the router and let it fully connect. 

Turn on the Play 3 and let it fully connect (white light).

Re-open the Sonos app.

See if that helps at all. 

Thanks for  reply. The above works initially (sometimes) but if I then try to change what I'm listening to i just get "something went wrong" flagged up without any suggestion of what I might do about it.