Blackberry Calendar version 18.104.22.16827 tentatively appears to have fixed the bug with frequency timezone change apps, whenever carrier connection changes.
Previously, the Blackberry Hub+ Calendar app until about version 22.214.171.12406 had a bug where the WWAN carrier switching (e.g. Sprint to T-mobile or vice versa) triggers a time zone change alert – perhaps several times a day! This used to 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 were subject to this fixed Blackberry Calendar bug.
Fix Blackberry Calendar time zone bug
Turn off Show timezone switch notification under Blackberry Calendar settings.