Check your history to see when the alarm was turned off. Perhaps you can match something up with the times its turning off In my case I have a rule see to automatically turn off the alarm when I arrive, via the keyfob.
I'm having an odd problem with my keyfob where it thinks I'm away but just in a room about 50 feet from the hub. When I return to the room where the hob is it turns the alarm off thinking I returned from being away. I believe that is what is heppening to me, perhaps you may be having similar issues. First of all, do you have keyfobs with rules attached to them? If so, that may be your problem too.
I forgot to mention that the history is the part of the problem also. Everything gets deleted in the history within about 6-8 hours. I don’t have any key fobs that could be causing this either. I can be Gone from on location only a couple of hours and upon returning the alarm will be disabled and all of the history has been deleted. It happens at both locations. This doesn’t happen every time, but enough that it’s concerning.
If you are on the free service then the history only keeps 24 Hours. It is supposed to anyway, but the app has a bug that has been reported for quite some time where it only shows history for the current day, only shows back to midnight of currernt day, not the last 24 hours as it should. You can get the full 24 hour history list by using the web portal, the official or unofficial. The unofficial might even be a bit better.