I cannot see any of my events in BusyCal, my calendar is suddenly empty
In BusyCal, the left panel displays a set of calendars that you have subscribed to. The checkbox next to the calendar name allows you to temporarily show or hide all events associated with the calendar. If suddenly all your events appear to have disappeared, ensure you haven't toggled the calendar's display OFF.
In case you have hidden unsubscribed calendars from view, you may wish to show these first (BusyCal View Menu > Show Unsubscribed Calendars).
BusyCal 3 supports two types of searching, Search mode and Filter mode.
1) Type Command-F to display a list of all matching results in the right sidebar. 2) Type Command-Option-F to filter your current calendar view to only show matching results.
You may have inadvertently switched to Filter mode, which would then only display events and todos that match the currently entered search term. Click on the search field and ensure you're not filtering on anything.
You can learn more here:
Smart Filters can be toggled on and off with a single click. Ensure you're not in a Smart Filter where the search criteria does not match any of your events and so all you see is an empty list.
More information on how to use Smart Filters can be found here:
Events gone. All events gone. Events won't show. Events not showing. Can't find events.