Just in case anybody reads this before attempting to relock the bootloader after reverting to Fairphone’s Android OS …
In case you installed /e/OS on your FP6:
Don’t try to revert to Fairphone’s Android OS for the moment, as you currently risk bricking your device when doing this, and as of now it isn’t clear why this happens!
What is clear is that you shouldn’t revert from the upcoming /e/OS 3.0.4 with the June security patch level to any Fairphone Android OS with May security patch level (see Fairphone’s release notes for this), because this would trigger Android rollback protection.
But /e/OS 3.0.2 was confirmed to have May security patch level, so this shouldn’t be the cause for the current brickings.
If you want to help to get to the bottom of this:
When in fastboot mode, run the command fastboot flashing get_unlock_ability before attempting to relock the bootloader.
Don’t relock the bootloader if the result of the command is 0!
Please report here if you get 0 as a result!
First try to get the OEM unlock setting enabled again in the Android Developer options and only try to relock the bootloader if back in fastboot mode the result of fastboot flashing get_unlock_ability is 1!
Please report successful relocking here (if you still dared relocking, brave soul)!