First of all, yes I have gone through droves of posts on XDA and frankly it’s a mess, but I can tell you that after following a few threads that just refer to themselves in loops, there’s no actual solution.

I have an LG US730 which was rooted and everything was great. I must have toggled something in SuperSU - I think maybe the option to be rooted during boot.

Anyway, now all I get is Security Error and it shuts off. None of the recovery power on switches will work. The only thing I could do is VOL+&- power while the usb is plugged in and it goes to a download in progress screen. Of course nothings happening and I need to remove battery in order to get this powered off at this point.

Anyway, I’d love if anyone has a tool to repair this. LG’s utilities all do nothing at all I think they’ve purged the back-end of older stuff so the programs that should download something and proceed simply wait forever.