HomePod sound keeps cutting out

I have a problem with BOTH my Apple HomePod speakers (one of which is a Mini). I play the music from iTunes (v12.11.0.26) on my PC and use AirPlay to Apple TV (Ethernet) and both HomePods (Wi-Fi).

The sound through Apple TV is excellent. However, both HomePods intermittently cut out. They will play the start of a song, cut out and then always pick up again for the last 5 seconds of the song. The next song will start to play, sometimes the whole song continues fine, but other times it cuts out again, only to restart for the last 5 secs of the song!

Although my HomePod Mini is new, this problem has always existed on my original HomePod. Now you could blame my Wi-Fi, BUT I have a Libratone ZIPP 2, which works absolutely fine ALL of the time. Also, I have tried moving the HomePods next to the Wi-Fi Access Points, but this makes no difference to the erratic behaviour.

Strangely, Libratone seems to have implemented AirPlay better than Apple on a device that costs about 3x less!

How do I troubleshoot this issue? It's so frustrating; I barely used my first HomePod because of this issue; I just assumed I was an early adopter, and it had a fault. Now I've discovered that even a 2021 Mini has the same problem.