The Blackberry Hub+ Calendar app currently (version 18.104.22.16843) 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.
Phones on aggregating MVNOs like Project Fi and Republic Wireless may be subject to this Blackberry Calendar bug.