Download mode disabled by kill switch on LG G3

I have installed CyanogenMod 13 on my LG G3 (LG D850), but I decided to return back to stock ROM. I download the files, but when I try to install by download mode, it shows a message that download mode disabled by killswitch. Regarding McAfee's killswitch, I'm using CyanogenMod ROM, and I believe it doesn't have McAfee as a preinstalled app. How to fix this issue? --- I am asking about third method so that I get some real thing to block this so called "kill switch" :(