Looks like 18.6 can consistently Play on all HomePods when using Scenes. I created a scene to play a particular playlist on all 10 HP. It has consistently worked since the update. The only issue is that some of the HP randomly drift out of sync with the rest of the HP playing. It does eventually corrects itself. Music will pause for up to 30 seconds to a minute on all of them, then start again in sync. Weird but it corrects the out of sync that can occur during the day. I have been doing this every day and just let them play all day up to 10 hours. Everyday it goes out of sync but it does the pause and play in sync again on its own.
