I was looking for “potential broken message id” in the log and noticed the unusual uid. Now that you say the timestamp is pretty strange indeed as well.
I would suggest you run kopano-fsck for calendar only without --autofix. If I remember correctly it will show you what it would fix, so that you can decide if you want to accept it or not.
There are quite some contacts with problems, so running without --autofix might be quite tedious.
Anyway, I think kopano-fsck should get you further in sync.
Is it actually an older installation with some updates of Zarafa/Kopano or have you migrated from some other solution?