Hey, I sometimes get this too.
It all depends on whether or not you're tired, I think. We don't all need the 8 hours, some more, some less. And it fluctuates. But if you're waking up with an alarm, sleeping in, and feeling tired during the day, it could slow your weight loss, possibly. It has for me. I don't know if it's the body hanging onto fat or water, but I always find after a busy period then a few good nights of uninterrupted, no-alarm-clock, wake up whenever you want sleep, the scale goes down a bit. I swear stress and tension weigh something too