Why did I lose all my calendar data?

[AC Question]

I lost all of my calendar data today. The only things still in it are some old tasks, but none of my events. I noticed it after setting up my gmail account by phone today, and also Google Drive. I restarted my phone, it's a Samsung Galaxy s4 mini, but it didn't restore.

 

[Golfdriver97]

Welcome to the forums. Were you using the Samsung calendar or the Google one?