My Calendar has disappeared

After installing eM Client 4.0, my calendar under Local Folders is empty, and the calendar I had been using so far has disappeared. Detail: I had also deleted my Sync2eM account.

I reinstalled my Sync2eM account and the calendar is back. I guess I don ́t understand that sync business very well…

I only have eM Client v4 installed. The calendar entries disappear, although they are still there in the Google calendar account. Sometimes they reappear when I do a Tools | Send/Receive All.