Since the upgrade a few days ago to One UI 5 on my Watch 4 the sleep recording is a mess...
1: Before the upgrade: If I woke during the night which I do a couple times usually for just a few minutes in the morning it showed the cumulative of all sleep sessions and in the timeline showed the awake periods.
After the upgrade: If I wake up during the night for a few minutes it assumes I am done sleeping and calls it a night and stops recording. It doesn't pick up any additional sleep sessions and append them to the record as it did before.
2: Before the upgrade: I would have about 1 to 1.5 hours of deep sleep recorded normally.
After the upgrade: Deep sleep is only showing as a few minutes never any more than that.
I see the watch 5 has the same issues... If I notice anything else I'll edit the post.