Calendar app giving notifications long after event has started

I have my work schedule and other personal events on my Apple Calendar and it syncs successfully between my Macbook Pro, iPad, iPhone, and Apple Watch. Occasionally, perhaps once per week and not on the same repeating event, I receive a notification hours after the event has started. While merely annoying, I am concerned that there will come a time when I am not notified prior to the event starting and will miss it or be late as a result. I always receive the correctly specified notifications prior to events. But the fact that I sometimes receive extremely late notifications from time to time is clearly a bug.