airplay 2 Airport Express and Apple TV same time

Just finished with Apple support. This is not supposed to work at all after the switch from Airplay to Airplay 2. It only works for a while because it takes a while for the system to recognize that it is using incompatible systems. Deselecting the computer just means it takes longer for the system to recognize the incompatibility.

By the way, I used to be able to play music to both the Apple TV and Airport Express connected stereos simultaneously before upgrading all operating systems/software in the past six months. Exactly the same equipment, network, iTunes account.... only the software changed.

I am back to square one and don't know what changed. Again, I can airplay from iTunes to either of the airport express units at the same time or both apple tvs but music won't play on either airport express and apple tv simultaneously. Any thoughts?

I just updated the OS for Apple TV and decided to try again to play Apple Music from my Mac on both an Apple TV (model A1625, tvOS13.2) and the Airport Express (operating version 7.8.1). It worked for a while and then stopped. The Apple TV is what dropped. When I selected it again from Airplay in Apple Music it started working again, but dropped after a while. I tried de-selecting the Computer from the Airplay list and it worked much longer, but eventually the Apple TV dropped again, but started up (again) when I reselected it in Airplay. The Airport Express unit kept playing music throughout these maneuvers. I am scheduling a call with Apple Support.

I was using a 2017 27" iMac. Your question prompted me to update the OS to Catalina and now at least one of the Apple TVs (the newer of the two) works. Thank you!