I have found that since moving to the 4.4.3 builds of Cyanogenmod M11, sometimes WiFi will "freeze" on the then-listed WiFi sites, and will not update the list of available WiFi sites. When this happens, the WiFi does not work either. Turning WiFi off and on doesn't help, nor does a rescan. The only solution is to reboot. This doesn't happen all the time; maybe 2-3 times since the nightly builds moved to 4.4.3.
Yesterday, I upgraded from cm-11-20140614-NIGHTLY-maguro to cm-11-20140615-NIGHTLY-maguro. I did this after the phone froze (screen off).
When the phone restarted after the upgrade, I discovered that the "wpa_supplicant.conf" file (in /data/misc/wifi) had been deleted, and a new, virgin wpa_supplicant.conf file had been created. This means that I lost all of my WiFi connection history (and passwords).
Fortunately, I have a backup of this file (dated 4 April 2014; somewhat older, but nevertheless quite helpful), but I haven't been able to reinstall it. When I overwrite the newly-generated wpa_supplicant.conf, verify the file permissions, and restart, WiFi won't turn on. I can switch it "On", but the switch stays gray (rather than blue) and the WiFi obviously does not work. If I then delete the re-installed archive wpa_supplicant.conf file and reboot (allowing a new wpa_supplicant.conf to be generated upon the reboot), WiFi works again without issue.
I've compared the headers of the archive and the newly-generated wpa_supplicant.conf files, and they are the same. The only difference that I am aware of is that the archive file is much, much more populated with data. I have no reason to believe that the archive version of the file is corrupt, as it worked fine (albeit, updated since April 6) until yesterday.
Is there a reinstallation procedure here that I am missing?