This is happening on my BlackBerry PRIV as well. I've been using an app for medication reminders for years, and I thought it was misfiring by giving reminders too early by four hours. Then when my calendar reminders also came on four hours early I realized it was the clock that was misbehaving.
The clock also changes back without notice and then the appropriate calendar reminder sometimes doesn't happen at all because it thinks the event has already happened.