Have you contacted Victrola’s Customer Support?
I’d be tempted to do a network refresh, by powering down all your Sonos devices, including both the Era 300 and the Victrola, then rebooting your router. Give it a couple of minutes to reboot, then plug back in your Sonos devices. Wait another two minutes, then open the controller, and check for ipdates, and apply them. Then test.
If it still isn’t working, I’d check with Victrola’s support folks first, then finally call Sonos Support to discuss it.
When you speak directly to the Support staff, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.