Everytime you click on a Movie XMM try to see if there are the movie files... except if the NAS or the external disk is not available (or XMM find it not available). In this case XMM will not try to search any movie file on this device until you restart XMM.
Can this be the problem? have you movies inside a NAS?
My movies are stored on an internal drive. All of them are at the same drive, except the rare ones that I have put on DVD's, and those are not the movies I'm having issues with.
For example,
A movie that I know is on my drive and linked properly inside the database. I can play it via XMM.
But after a while, I can't keep the track of why, the play button goes off / disabled, for all the movies in the database. And I can only fix it by restarting XMM.
Is it possible that the drive goes to sleep or something? (Internal SATA) I didn't configure anything like that but I'm just wondering?