HomePod can't find music in my library

All our iPhones, Macs, and HomePod minis are on the latest OSes. But for probably a year now, HomePod mini can no longer find music in either my library or my wife's. Playlists we know we have, artists we know we've added, nothing. The response is always "I couldn't find X in your library. You can try asking for..."

I've hard reset all our HomePods multiple times. I've been through all the settings to make sure they can recognize our voices. I've made sure she is set as the default user on her office HomePod.

This has become quite frustrating. Our HomePod minis completely fail at one of their core reasons for existing.