I haven't previously had issues with the auto-detected sleep, but I usually try to make sure to manually activate sleep mode. I forgot to turn on the sleep mode two nights ago. I kept checking throughout the day yesterday, but the sleep period never registered as "detected."
I did notice a strange thing when I was looking for my detected sleep. The last detected sleep was from the morning of 6/1, but the strange thing is that there are two sleep periods recorded for that date that overlap. One shows from about 12:30 to about 5:15 when I woke up to let my dogs outside. The other shows about 12:30 to about 7:00 when I was actually waking up for the day. The graph that shows times I woke during the night match up, so the same data was used.
I don't know why the first sleep session was reported since the analysis of the data recocgnized that my sleep session lasted another hour and 45 minutes.