Call Apple, they will have you submit some logs like they did for me, then someone from the health team (I’m all but sure that’s the department he said he was with when he called me today; was doing some yardwork and didn’t catch it other than “health something or another”).
He sent an email with a link to some diagnostics app that installed on watch and phone - it told me to press and hold crown and power and wait for a little “pulse” indicating it was compiling logs or whatever, but instead of doing it for a second or two, I kept them pressed, forgetting that hard force restarts. Took a decent amount of time to boot again and when it did, I opened the health app and ECG setup was back, and prompted me to install the app on the watch.
He said it could have been a fluke working for me after the hard reset. He also said they have been getting calls about it and getting logs as they’re not yet sure why it’s happening, and want to get it fixed. Hopefully they can get it squared away for you.