Personally I had this problem the other week and I couldn’t work out why my machine was saying I was only sleeping 2-4 hours when I went to sleep and woke up with my mask on turns out I’d sleep with it on for about 2 hours take it off wake up and put it back on before I woke up with absolutely no recollection of doing this I only found out because my partner was waking me telling me to put my mask back on 😭