Random "Modified File" message in FCPX - Offline Media.

I'm being hit by a random media getting offlined by FCPX. The Clips show the Message: "Modified File", even though nothing changed to my knowledge.

Relinking doesn't work, weirdly. FCPX shows the proper file name, but trying to reconnect to the actual media does not work.

I thought of re-importing and manually replacing the clips, but what seems to miraculously work is to actually drag the offending media file from the Finder into the Browser.

All of a sudden the media gets recognized and the clips are re-linked and online again.

Quid?