Me too. Adding my experiences so Apple devs can troubleshoot this. I have multiple connected calendars including Exchange and iCloud. Everything worked as expected before Sequoia, reliably and consistently. After Sequoia the following happens consistently: 1) invites takes a very long time to appear in the calendar (like an hour), 2) it is virtually impossible to add a new meeting manually to the calendar. Edits show in the meeting but do not move to the calendar view, including the event name, the selected calendar color, etc., 3) when editing an existing meeting the app freezes until the edits are discarded or the meeting being edited is deleted.