New Airsense 10 sometimes missing mask-on hours

[cpap450]

I recently replaced an Airsense 10 that had >20k hours on it, with a new one - still Airsense 10. And two times in the five weeks I've had it, it has credited me with one hour or less of usage, even though I always use it 7-9 hours nightly. That's the reason I replaced the older unit; it worked fine except a few times a month it was crediting me with way less usage time than normal.

25+ times a month I'll only take the mask off upon wakeup. The other times, I'll go to the bathroom once, but then put the mask on.

What's going on? On the one hand, the machine helps me sleep and keeps me healthy, and that's all I care about. But on the other, if one little thing I can see is wrong, what about other things I can't see? And I'd like my sleep doctor to have a 100% accurate representation of my usage.

And the unit usage on this machine, seen from the settings, is <400 hours.

[mlmollenkamp]

Have you checked that the machine is set to the correct time? especially am/pm? Resmed starts a new day at noon so if am and pm are swapped it will start a new day at midnight rather than noon. This can also be an issue for late sleepers who arise after noon.
If the time is correct I'd probably try the option to erase everything and start over.