Music just doesn't sync well across my devices. Full stop. I can start playing something on my phone, select my Homepods as my speakers via Airplay, and it will play. But if I lock my phone and come back a few minutes later, it'll forget what is currently playing on my HomePods and make me "replace" the music. If I try to control it from my other devices it's the same story. More than once I've had it yell at me for trying to play music in more than one place at a time and try to get me to upgrade to a family plan. I'm single and live alone.
Siri also often misunderstands scene names. I just turned to one of the HomePods and said, "Hey Siri, activate 'Nightlights Only'" (a scene name). She said, "Good night." and did nothing. This happens no matter how well I enunciate (general American accent) or how many times I try.
In the process of messing with it just now to prove my point before sharing, Siri hit a snag and told me to go update my iCloud account in the home app, so I did and ran into the same problem as this user[0] did two years ago (disappearing password prompt). It's wild.
This is not the Apple that made iMessage and Messages in OS X the most seamless text messaging experience I've ever experienced before.
[0]: https://www.reddit.com/r/HomePod/comments/jsw122/homepod_upd...
Edit: I had my iPhone’s wifi off. Apparently I had to be on the same network to resolve the iCloud issue. Why not mention that?