It happened to me too after the WordPress update. For me, it was a conflict between another plugin and the calendar. I went through one by one, turning off (or deactivating) each plug in to find the culprit. I decided it was a plug in I could live without so having it turned off solved the problem.
I think it had to do with a WordPress update that happened a few days ago. Our calendar blew up also. I deactivated then reactivated the plugin and got my data back. I also clicked on the ‘search for updates’ button that is present in the plugin window for Timely.
