The bug occurs when creating\ a recurring appointment. When you create 2 alerts, only 1 is kept. So if I create a first alert for the day prior to the event, and a 2nd alert 15min before the event, the alert for the day before seems to be swapped and is kept, but the alert 15min prior to the event never takes place.
I called Apple Accessibility, and she could reproduce this w/o using VO. Furthermore, evidently no one had reported this, so she began a new bug tracker on it.
Just sayin, cuz I thought it was either VO or me being stupid (is the latter even possible? Yes, unfortunately so). Have a great rest of your day, all.