Hello @Fanlight
It's hard to guess why your device didn't record the last 3 hours of your sleep.
Every now & then, my device doesn't track my sleep properly. When that happens, I use the following workaround. I edit my sleep log to have the correct wake up time. After I correct my sleep log, it may take a couple of hours for the Fitbit app to update my log with my sleep stages & sleep score.
This process also works when my device breaks up my sleep into more than 1 log. I note my correct sleep and wake times, then correct the times for my sleep log in the app. It often requires me to delete one of the logs so I can combine them into a single log. It took me awhile to accept that when I delete a sleep log, I'm only deleting a time interval, not the data that my device tracked during that time. My corrected log will show my sleep stages & update my sleep score.
Rieko | N California USA MBG PE
Best Answer