Spotify doesn't see Sonos

[evenmorecowbell]

Hi,
I have two Sonos systems, in the office and at home. Both are authorized to access the same Spotify account.

I can access both systems using my Sonos apps (both iphone and desktop), but I cannot access the office Sonos using my Spotify iphone app (the desktop Spotify app works fine). At home, both desktop and iPhone Spotify apps can access Sonos.

What can I do? I tried restarting the router, Sonos, Spotify app, iPhone, reauthorizing Spotify access - all to no avail.