CM12.1 - My lock screen is not working at all! I recently updated to the CM 12.1-20151024-NIGHTLY-d851 build (I have an LG G3, D851) and also flashed gapps with the a recent "nano" version. Since then, I have noticed that the lock screen does not work at ALL. Whether I choose PIN or swipe or whatever, it will not lock the phone. (The option for "none" disappeared too, but it became available again after removing an active guest session on the phone.)

I've tried rebooting the phone after choosing different lock screen settings and enabling the PIN again. I also tried updating to 12.1-20151101-NIGHTLY-d851 (thinking maybe it was a nightly bug that got fixed). I also reverted to the earlier working version of gapps, but that did not help. And let's not mention the other "solutions" I stumbled across via Google which did not help either. The phone simply will not lock at all. This is driving me crazy.

The only thing I can think of is that it MIGHT be related to an error I saw while flashing my phone during the upgrade: unable to mount /radio (or something like that).

What can I try next?

EDIT -- UPDATE: The other day my lock screen started working again, without me having to change anything. I suspect that the problem was due to some type of app that has an ability to block the lock screen (for example, I think Google Maps can disable the lock screen temporarily so you're not fiddling with unlocking your phone while driving, as that would be rather dangerous). I'm guessing some app (hopefully not malware!) was blocking the lock screen and got updated in the background, and it started working again. I have no clue how to verify this. At least I did not have to downgrade or flash back to an earlier builld. I am presently running the 12.1-20151104-NIGHTLY-d851 build.

EDIT #2 -- UPDATE #2: I just noticed in my quick settings (i.e. the pull-down from the top of the screen) that there is now an icon to turn lock screen on/off. I guess this is a new addition that I failed to notice, and 99% sure this is what caused the "problem" -- which was really a feature. I must have accidentally tapped it off and then back on before even noticing it was there.
Answering my own question here, so I can mark it as the solution. (I also posted this in the original question as EDIT #2).

I just noticed in my quick settings (i.e. the pull-down from the top of the screen) that there is now an icon to turn lock screen on/off. I guess this is a new addition that I failed to notice, and 99% sure this is what caused the "problem" -- which was really a feature. I must have accidentally tapped it off and then back on before even noticing it was there.