[Plugin: Sync Facebook Events] Events imported multiple time

Every time I do a sync, the event data is imported multiple times. Here a brief description:

first sync:
events are imported twice, once for author “admin” and once for post_author = 0

every further sync:
will do the same, so after 2 syncs each event is listed 4 times in the backend

3. on the website each event is displayed, correctly, only once

Any idea?

Thanks.

https://www.ads-software.com/extend/plugins/sync-facebook-events/