Default CM11 randomly freezes

Installed the unofficial CM11 for my z1c 24 hours ago. It worked well for the first 12 hours. But the phone periodically freezes after periods of idle.
If I haven't used it for anywhere between 20-60 minutes, it doesn't unlock, stays dark and I have to force a reboot. This has happened 4 times in the past 3 hours.
I'd post this directly into the CM11 thread, but new users can't post in that thread.