Rekordbox all library data randomly deleted

Hi!

Yesterday, after normally closing Rekordbox like I always do, I opened it after a little while again, and suddenly my entire collection, cue points, grids, playlists, preferences, etc were gone; basically as if I opened Rekordbox for the first time again. 

I also got a notification when I opened it, which I unfortunately can't remember exactly, but somewhere along the lines of "Failed to communicate with ..."

I coincidentally made a backup a few days ago (without music files), but when I try to restore my collection, I get the notification "Failed to restore collection" 

My music files are on an external USB, and they are fortunately still there; just all the data that was on my Rekordbox is completely gone - literally looks like a factory reset of Rekordbox, even though I didn't do anything of the sort. 

I use version 6.8 if that matters. Also I did close and open Rekordbox more than 3 times already unfortunately since this happened.

Can anybody help me please? I don't really know what happened or how to fix it. I'm happy to answer any further questions ofcourse.

Thanks in advance!