Sorry, I think it is bricked 
I still don’t know how “Allow OEM Unlocking” got disabled, but I think it had to be when you reinstalled FPOS. Regardless, as that seems to have been disabled one way or anther before installing iodéOS (even if the device wasn’t locked), then when installing iodéOS, locking and then hitting a “won’t boot” issue it is now a brick You will need to see if it can be reset by Fairphone.