I had these same issues on my V1 hub. I had to disable my SmartAlarm because it got so annoying sounding the siren and sending me false alerts.
I discovered in my situation that the problem was related to the automatic “Hello Home” actions (now Routines). I could run them manually and they would work so long as they changed the home modes away from the current mode. If they were scheduled to operate based on some automatic condition, then they would only change the house mode, but wouldn’t notify other SmartApps of the mode change event and therefore in my case, SmartAlarm never received notice that the mode changed in order to change it’s armed status. I could go into SmartAlarm and hit done (or manually run a routine which changed the home mode away from the current mode and then another routine to change it back) and SmartAlarm would then see the new mode but the main issue was the mode being changed by automated routines which didn’t send event notices to apps that were subscribed to location mode changes.
When my V2 hub came in, I had to delete everything (including my home location, which wouldn’t delete, so I renamed it to DeleteMe) and create a new location, then reinstall all devices and setup all new routines and SmartApps in the new V2 location. Fingers crossed, automatic routines and associated SmartApp event notices have been working for 2 days now and I’ve been able to re-enable my SmartAlarm. My other SmartApps experienced the same issue and are now receiving the mode change events and working as expected.