Hello (sorry for my grammar),
I had the same problem with one of my HomePods.
The problem occurs when there are multiple access points, or one access point with enabled 2,4 and 5 GHz Wi-Fi in the household (or weak Wi-Fi strength. RSSI -60 to -85 dBm).
The HomePod every X minutes (I don’t know the value of the X) scans the “network” and connects to the strongest signal.
After several connection “attempts” (example: for 10 minutes the 2,4 GHz signal is better, after the 5 GHz one. More access points more “roaming” for the HomePod) the HomePod cannot connect to the Wi-Fi anymore (software glitch?), and only the reboot helps.
What I did: (I have 2 access points). Disabled the 2,4 GHz band on the first AP (the 5 GHz is on) and the TX signal is set to 100%. On the second AP the 2,4 GHz and the 5GHz is on, but the TX signal strength is set to 20%. This way my HomePod stays connected to one AP and one band.
I hope this long and boring explanation will help you.