Sync stuck in a loop

For a couple of days, without having changed anything to the setup, the sync of the folders starts and gets in a never ending loop. I still can access the (or some of ) options in the menu but cannot read any email (old or new), nor write any new email.

The Windows Task Manager shows no activity in the “working set memory”, and the “I/O reads” does not change.

In other words, I cannot use EM any longer. Any idea on what’s happening?