I usually sleep from about 10 pm until 6am. It's really common for my Fitbit 6 to not record sleep until after midnight. Any idea why?

ECG monitoring is probably the standout feature for this device. Otherwise any cheap HRM will do the job. I would like to know if its irregular heartbeat detection is as good as Apple Watch. I know two people who were notified of major conditions, one had to get a pacemaker, just by wearing an Apple Watch. So this should be an ordinary feature that people can rely on across brands.