I've had this happen, though not regularly. Usually, a lack of details means Fitbit thinks you slept less than 3 hours. Sometimes I find that if I wake up in the middle of the night and stay up for a while, Fitbit will decide to completely ignore either the time before or the time after. I very frequently wake up an hour or two after getting to sleep, and Fitbit often (but not always) decides to ignore that initial "nap".
The first thing I check is that the start and end times for the night look reasonable; and, if not, I edit the sleep log. Fitbit will analyze all of the sensor data for the new sleep times, show the detailed info if your total is now over 3 hours, and generate a sleep score. (Sometimes the sleep score doesn't show up until I go back to the dashboard.)
I really like the Fitbit sleep tracking; but sometimes it's a bit flaky.
I'm currently using a Versa 2 as well, but it's more a "Fitbit thing" than a Versa 2 thing, because I've seen the same quirks with other models.
