Sleeping not measured properly

[Covo]

Two nights in a row the sleep is measured first until around 3 am, then it restarts an hour later. As a consequence it measures two periods of around 3,5 hours sleep instead of one period of 8 hours. What can be the reason? Can I fix this? Would it help to set the sleep measure on ‘sensitive’?

[M0rtyC]

My sense begins tracking my sleep 2+ hours after I go to bed.   I must be superhuman to consistently function on 4.5 hrs sleep.