Community member PAB from June 11 seems to have the same problem,
Calendar reminds accurately of an activity with a banderoll. You have 2 options. You can either press the snooze button on the left to be reminded later, or you press the discontinue button on the right.
The discontinue button on the right side of the banderoll does not work. I have emClient in the system tray with latest updates and have configured the software as standard software in windows.
Hope to solve it in the community!