Re-paired my phone, causing problems.
Got a new phone, and was surprised everything was working without even pairing with the new phone! Then I had to mess all that up because I wanted to use the watch to keep the phone unlocked. It said I would lose all health data, and I did!
But now it's not recording my heart rate or my sleep. Syncs okay, measures steps okay. Everything seems set correctly in heart and sleep, but no data after two days.