The problem is not your own setup - the fact that Intel is still huge in the server market (and very likely will be for a long time as AMD still is not up to their level in some applications) is the concerning issue.

Have a look at mDNS. It’s very often the issue here.

If you use home assistant take a look at music assistant, it solves a lot of these issues for free.

Sadly you still need that POS to intially configure it and the occasional update.

That very much sounds like a network problem.

Are both hosts in the same subnet?

Well, we did learn exactly that in school and had a practical demonstration at a museum.

But on a different continent.

Just as a way to soothe the outrage about this POS of an app: A fair share of the problem can be minimised by using Home Assistant and Music Assistant to control the Sonos devices. This way you very rarely need to actually use the app anymore.

Which is good because it’s indeed shit.