Chromecast Audio and AP Isolation problem

I have 14 Chromecast Audio on my network. They are in 2 different locations.

Some connect to the 2.4 GHz band, some to the 5 GHz band.

In addition, some connect to the Orbi router, some to my first Obi satellite, and some to my second Orbi satellite.

When I use my smartphone connected over Wifi, the Google Home app sees a random number of Chromecast Audio. Sometimes 0, sometimes 5, sometimes 12. Never all 14 .

If I use a wired PC, I can ping the IP address of all 14 Chromecast Audios, so I know for sure they are all connected to the Wifi network.

I also have a ping app on my smartphone, and if I use it, I can only ping the IP a few of the Chromecast audios from my phone, without any pattern that I can tell. This explains why the Google Home app cannot find all the Chromecasts either.

Based on this thread , I tried to set the "Allow guests to see each other and access my location network". It did not make any difference for this problem. I'm not surprised, also, since I don't have the Guest network enabled, and my Chromecasts are connected to the main Wifi network.

My Orbi is running in AP mode. Router and DHCP server is R7000. I reset my Orbi to factory settings today. The only thing I set which is not default was to use AP mode, set the SSID, password, and the attempt to set the "allow guests to see each other and access my local network" option (which is now off). Still, the problem is the same.

Are there any settings that will work for multiple Chromecast ? I have spent so many hours with so many problems with Orbi, I'm at the end of my patience.

 If I use my R7000 wifi (standalone unit) instead of Orbi, I don't have any problem, but of course it's a single AP, not mesh.

If I power off both Orbi satellites, then my smartphone can see all 14 Chromecast Audio successfully. But of course, that is not a solution, and really defeats the point of Orbi. At least, this rules out any issue between Chromecast being on different wireless bands - it is strictly the case that if some Chromecasts are on different Orbi (router or satellite) then a smartphone cannot see all the Chromecasts on the network.