The problem is that the select which gets all PENDING events is run at beginning of cronjob, but event status is not checked when every event begins sync.

Scenario:
. cronjob A start, selects all pending events: 1, 2, 3
. cronjob A starts syncing event 1, but network issues make this a long process
. cronjob B starts, selects all pending events: 2 and 3
. BANG! error because both processes will try to sync event 2 and 3