When the HomePod first launched, it did not count at all to Apple Music streaming limits. You could have two HomePods playing different music, and start a third stream on your iPhone, all playing at the same time. Now, it seems that only one HomePod can be used at a time. I can play something on my phone, and something else on the HomePod, but if I start another HomePod playing, the first one stops. Has anyone else noticed this?