Well, there's nothing in there that looks obvious to me, though all of those "screen change" and "screen resize" event are suspicious. That may be unrelated, though.
Is there anything in the logs complaining about DPMS? From the log you sent, it appears that the X server is, all by itself, deciding not to power off the monitor. I don't know why. If you find a section of the log covering a time when the monitor had been powered off, and then powered back on, without you having made an attempt to unlock the screen, that might provide more of a clue. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org