This is happening with the calendars on this page: https://extranet.atlassian.com/display/MAR/Confluence+Family+Product+Blog+Schedule
It seems that kick-ass has disrupted some of the saved filters. What this looks like in Confluence/TC is an empty calendar, with no indication why. My assumption was that TC was broken, but it's actually an error on JIRA's end.
It would be helpful to know, so I could go into JIRA and fix the filter.