Try powering the Move off completely, not just asleep, then reboot your router. Give your router a couple of minutes to finish reloading, then power back up your Move. 

I had the exact same issue with my Move about 3 weeks ago, after working for years.  My set-up may be slightly different as I use SonosNet for most of Sonos system but the Move for obvious reasons uses wi-fi. 

The way I sorted the issue was to remove the wi-fi credentials from the Sonos App and renter them.  Even though they hadn’t changed, this appears to have resolved the issue but I can’t work out why or how!  (I have reserved IP addresses in my router set-up, so it can’t have been a duplicate IP address issue!)

UKMedia, 

Thank you for your input. Not sure but think my move ended up between two mesh transmitters when I moved it to the porch. I had an extra transmitter/extender so I put that between and the problem went away. 
I could probably just have blocked the move in one unit and that might have fixed it too. 
 

I assigned a static ip like UKMedia mentioned and that seems like that works. I moved move to the other end of the house and it stays online now. 
it was strange that it got offline but still played. 

Turning move all the way down and startup will connect move again as long as it stays on that connection.