It’s acknowledged and being worked on. Has to do with port numbers and UPnP. If you have more than seven Sonos and/or Chromecast zones, you see only seven and then you see no other zones. If you want a temp fix, disable Sonos zones until you get under seven until they fix it, at least that worked for me.
Here’s the thread where they are working it, if you want to get into the networking underlying the issue its linked to in there. You have to read the whole thread to get to where they’ve diagnosed it and acknowledged they are working on it.