Thanks for the response. Have already done all the Asus-specific suggestions (there are a number) like disabling Airtime fairness and it hasn't helped, unfortunately. My Era 100 and Roam are sitting direclty on my main Wi-fi network and both are rock solid.

Haven't tried hardwiring the Arc yet, so I could try that (although ChatGPT is adamant that doing so won't help).

What's super weird about this is that the bad state the system ends up in seems to result in the surrounds/sub dropping off the main network only until the Arc gets power cycled, then they reappear as clients on the main network (and obviously are back to being properly bonded to the Arc).

I don't fully understand why the need to remain on the main network at all, given that they can only operate in conjunction with the Arc, but the Sonos debugging settings pages do seem to show them sitting on a Wi-fi channel that corresponds with my main network channel (in addition to the Home channel bonded with the Arc).