Using Outlook for Android for personal email and calendar management
I can confirm the problem noted by @ab1280 is occurring in other installs of Outlook for Android. My install is version 4.2310.0 (42310816). In my case, my implementation uses Company Portal (ver 5.0.5823.0).
I have not yet found a solution for this problem, which appears to be a new one.
In the past I've had very little trouble synchronizing the Outlook calendar to my phone's Android calendar. However, I've recently experienced multiple instances where the setting to sync Android calendar (in the Outlook Android application) has seemingly inexplicably changed its setting to disabled. The result is the synchronized Android calendar is deleted from the phone.
Let me reiterate that, when the setting is enabled, the sync to Android calendar appears to work just fine. However, that setting which enables sync to the Android calendar doesn't "stick." For some reason, it's switching to disable the sync, without user interaction.
In my case, I use a third-party calendar application to display calendar notifications (the notification and snoozing functionality available from that third-party application are much more robust than those available on the Android Outlook application). When the synchronized Android application is deleted, apparently without user selection, the result is user is not notified of upcoming appointments. This is a serious matter.
Microsoft support will tell me to provide this kind of feedback from within the Outlook for Android application. However, my employer has disabled that capability.