Crashes when sleeping

When I sleep, about 1 time in 20-30, the game fades down to about halfway through the 'fade to darkness' animation, then freezes, then after a few seconds quits unceremoniously to the Mac desktop. This has occurred (unpredictably) for at least the last dozen weeklies.

I carry a bed with me at all times, and sleep wherever I happen to be when it gets dark, so this occurs in many locations. But I've never yet spotted any more of a pattern than that.