Video Icon / Thumbnail is black (in Finder)

Please watch this 45 second screen recording. This issue happens occasionally when exporting from Final Cut Pro X.

I am curious if there is something I can do in Final Cut (before export) that can prevent it?

Or something I can do in the Mac/OSX/Finder Settings that can fix how it is displayed?

www.dropbox.com/s/9acc94ex48hrbf5/Video%...ut%20Export.mov?dl=0

Unfortunately you can't set the poster frame for the file in FCP. If you can use Send to Compressor that has an option in the Viewer to set the poster frame for the exported file.

I dont have compressor.  But it just seems strange how the poster frame can be solid black when there is never a solid black frame in the entire video?

Is there something I have in the timeline / editing process that's causing this?

Could be corrupted Finder cache for those particular files. See what happens if you export 30 secs of each file or view the thumb on a different Mac. (Had that happen once due to a single black frame at the beginning of the file I never noticed.)