The Blackberry Hub+ Calendar app through version 18.104.22.16806 has a bug where the WWAN carrier switching (e.g. Sprint to T-mobile or vice versa) triggers a time zone change alert. This can happen several times an hour in particular locations, say a thick metal building with Sprint and T-mobile towers at opposite ends. Walking from one side of the building to the other can trigger a switch from Sprint to T-mobile–with this bugged Blackberry Calendar app, each switch triggers a time zone change alert. This 22.214.171.12406 seems to have greatly reduced the number of calendar timezone alerts, but they still happen a couple times a day (down from several times per hour).
Phones on aggregating MVNOs like Project Fi and Republic Wireless may be subject to this Blackberry Calendar bug.
Fix Blackberry Calendar time zone bug
Turn off Show timezone switch notification under Blackberry Calendar settings.