Sonos subscriptions failed - Sonos device cannot reach Home assistant at port 1400, yet it is reachable and everything works

I recently noticed I’m getting “Networking error: subscriptions failed” for my Sonos integration, and it is falling back to polling.

“Sonos device at xxx.xxx.xxx.xxx cannot reach Home Assistant at xxx.xxx.xxx.xxx:1400”. I can telnet to port 1400 on the HA vm. the vm and the speaker are on the same subnet. Everything Sonos-ish works otherwise. No idea what to look at since 1400 is definitely available.

suggestions on where to start?