1 Playlist not connecting to Sonos device

[Enwrapped99]

Plan

Premium

Country

US or New Zealand

Device

PC

Operating System

Windows 10

My Question or Issue

I use Spotify basically every day as I work from home. Have 3 main playlists that I use. 

I connect to Sonos speakers.

Have 1 playlist called Pop Collection. Just recently I stopped being able to select the Sonos device - but only on this playlist. The other 2 I can still select the deviceand it accepts command. Device shows when using Pop playlist but for several days now I just cannot cannot get it to activate.

Pop does work fine if I play on This Computer.

Bit more info. Just tried an additional playlist outside of main 3. Works ok. 

Even if I select the device first in another playlist and then switch back to Pop and click on a song it will not play that song or any song while Sonon selected.

NB. In case relevant Pop is largest playlist at 5226.