If you have a Mac. There is a bug ticket in for recurring past notifications & a workaround in the meantime you can do till fixed. See @Gary post end of the below thread for workaround.
Ps Hopefully there will be an update soon.
Calender reminder/notification keeps popping up even if event is from past - Calendar - eM Client
Go to the Calendar section of eM Client and switch to the Agenda view. You will see the icon on the toolbar after Day - Week - Month.
Uncheck “Hide Past” option by clicking on that icon. You should be able to see all your past events.
Select all events for which you want to dismiss notifications.
Open context menu by right clicking any of selected events and chose Reminder > No Reminder
You will no longer get reminders from past events.