When loading an event page from your calendar, you recieve this 403 Error:
Something went wrong while fetching events.
The request status is: 403
The error thrown was: Forbidden
Do you have a plugin installed called iThemes Security Pro?
It's could be a setting in that plugin. The one that triggered it for other users was: Suspicious Query Strings - Filter Suspicious Query Strings in the URL. Unchecking this option fixed the problem.