HomePod as speakerphone won't connect or drops calls

I am having serious issues with my HomePod refusing to connect to my iPhone during phone calls, dropping audio during calls, or dropping calls altogether. I am running the most recent operating system version. It's become pretty much unusable at this point.

My WiFi router for this HomePod is an AirPort Time Capsule. I just had to replace an old AirPort Extreme in another room because sessions with connected WiFi devices would repeatedly hang. Could the Apple router be causing these issues? It works OK with my iPhone XS, but perhaps there are problems with other WiFi hardware.