screen freezes randomly

Occasionally, whether on the title menu or in game, the screen will freeze.
The game still runs, sounds play, menus click, window can be moved etc.
But no more frames,
Not 0 fps either, (waited forever once, it didn't ever right).
And if I try resizing the window the image just gets cropped off.

If it happens again I'll force crash and drop you latest.log and the report.

EDIT:
I should note that when this happens, it takes several minutes even an hour of run time, to manifest.
Dropping the crash report and latest.log...