Hi Maki,
Sorry to hear about your issue with the Apple Watch Series 6 ECG Monitor. How frustrating! Here are a few tips to (hopefully) fix the problem.
- Close and re-open the ECG app.
- Turn the watch off and back on after 1 minute.
- Clean the digital crown. Run the crown under room temperature water and spin it as you do so. Dry thoroughly at the end.
If the ECG still does not work, reset your Apple Watch. This is annoying, yes, but can eliminate software glitches. That is the most likely solution if the 3 steps above don't work.
Reset:
Watch iPhone App > General > Reset > Reset Sync Data
If this does not work, erase the Apple Watch and set it up again as a new Apple Watch.
Erase and reinstate:
Watch iPhone App > General > Reset > Erase Apple Watch Content and Settings
If all of this doesn't work, take your watch to an Apple Store to talk to professionals. I hope this helps you and I will follow this thread if you have any further questions I can answer! Be well and happy holiday season.
All the best,
Justen