My accounts disappear when I reboot or update my Android device
This issue is caused by an Android bug (not Team Calendar Sync).
Not all devices experience this issue. Actually only a small subset of devices are lucky enough to have the Android bug.
The issue causes your Team Calendar Sync accounts / calendars to disappear when some devices restarts or updates. I have published a free app that fixes the issue for those who experience it. The free app is call "Team Calendar Sync Workaround". Once you have the free app installed your accounts will no longer disappear.
As I mentioned, the issue is caused by a bug in Android (not Team Calendar Sync). The issue effects all paid apps that use custom account types. Not all devices are affected, however; it depends on your version of Android and your wireless carrier (some carriers have pushed out a fix).
There is more information on the free app page here: https://play.google.com/store/apps/details?id=com.teamsite.android.calendar.workaround.generated
Download the free app Team Calendar Sync Workaround