One not-so-rare network issue is if you have a separate wifi router connected to your primary ISP router. A common mistake would be to connect your ethernet network directly to the ISP router. If you do that, and have airplay clients connected both wirelessly and through ethernet, then you've created a situation where Airplay will have to work between your ethernet network and wifi subnet, and it doesn't do that well at all. So best practice is to either have all of your airplay devices connected to your wireless network (via wifi or hardwired to the wifi access point), or to run your wifi in bridge mode.
Also, it's more specific than an Apple problem - it's a HomePod and HomeKit problem. I have no issues airplaying lossless music to a combination of wired and wireless speakers, including Sonos, AppleTV, and airport express. I did have problems when there was a HomePod in the mix, and as mentioned earlier have never had luck getting HomeKit to choose speakers. HomePods are a poison to your airplay network.