Edit: Saw a similar post and solution suggested here.
Been working the midnight shift since June. Since then sleep tracking has only failed by tracking some nights completely. Last week I changed my sleep schedule to solve this and that's when the following happened, but not instantly.
My Sleep Schedule for a Midnight shift:
Sleep tracked normally. Went to sleep on Saturday, woke up on Sunday.
The next "day" going to bed on Sunday, woke up on Monday. (Notice two different sleep hours)
Then on that same Monday by 5 pm-ish and waking up at 10pm. Both photos taking on Tuesday (12am) at work.