Hi there,
I have a similar problem than this guy (
) on my FP6 Android stock. I installed E /OS yesterday so no compatibilty problem with security patch, and I was able to relock the bootloader safely, but as it was not mentionned anywhere in the command line tutorial I didn’t disconnect from google account and now I can’t set any option to lock the screen.
I saw that I needed to go back on Android but as him, impossible to enable OEM option from Murena OS, it just make settings crash. So I can’t roll back.
As I said I am on FP6 with last official e OS build, every other things seems to work properly.
Any known solutions ? Can it be fixed by future uptade ?
Thanks for help 
Did you try to unlock using adb? The e foundation outlines how to here: Enable USB Debugging and OEM Unlock .
Though having said this, the latest version of FPOS FP6.QREL.15.162.0 has a lower security patch level than e/OS 3.4, so I wouldn’t attempt a rollback, but I am unsure how it works. Perhaps someone more knowledgeable than me can chime in?
Yes I tried but it seems that this method doesn’t work on FP6 and I can confirm it.
I am able to go trough bootloader, fastboot devices detect the phone, but then fastboot oem unlock or oem allow-flashing are both returning failed, unknown command..
I think that on FP6 the only way is from the settings menu 
Then if I am understanding good, I can roll back even if security patch is older, I just can’t relock the bootloader or it will brick the phone. But it’s only the next step if one day I can enable OEM option again ^^
Thank you anyway