Hi @DanMtsn,
What kind of device did you start playback on before the Chromecast zone? I just tried migrating zones from a Dragonfly Red, Pulse 2i, Chromecast Ultra and Toshiba Built-in Chromecast and I did not experience any crashing.
Have you managed to replace the old router or are you still using that one? I suggest replacing the router first, as these symptoms might also be due to your network.
As for specific router models, we cannot provide a specific brand/model, but as you have seen there are quite a few threads that discuss user’s experience with various router brands and models.
We have found that often ISP routers have poor multicast implementations, but that is obviously not noted in the marketing materials for the router. Mesh is a good choice if you have a large area you need to cover.
Once you replace the router, we can see what issues are resolved versus which ones still need further investigating.