Deleting an event instance

If you go to https://mealsonwheelsplus.org/daybreak-adult-day-center/calendar/ and then advance to May, you will see a calendar of events. Recently, when you go to a repeating event, and View Scheduled Dates, and delete one instance, it deletes all the dates except the start date. In this case, I am looking to delete the instances of a weekly event on May 29th since it is Holiday and we are closed. This has worked in the past, but has now begun to have this issue. Thanks for a great plugin.

The page I need help with: [log in to see the link]