This morning I woke up and Garmin Connect says no sleep was tracked even though I have been in bed from 8PM till 4.30AM. I do see heart rate for the entire night, so data was definitely tracked.
Granted, it was an unusual night where I slept a lot worse than normal, was having a slight fever and my resting heart rate was around 20 bpm higher than usual because of it.
It's very annoying though since these kind of outlier nights are exactly the ones that should be tracked properly to inform all downstream metrics such as training readiness (which right now does not even give me a number).
(Been wearing it for 3 weeks now and apart from the very first night, it did track all other nights)