I was having issues with the rpmfusion version of motion with Fedora 20 crashing late at night. I figured out that it was crashing when log-rotate would run. I think this was only happening when motion was recording to a file at the same time logrotate would run.
Motion was using it's own log file. /var/log/motion.log
, I took that out of motion.conf and just let it log to /var/log/messages and the problem went away.
The log file was deleted and I've updated to Fedora 21 since then,
but I recall it said it could not find motion to restart.