I have just upgraded my FP5 to the latest official build to get A15. I resorted to the manual installation after the web installer only got me to A14 (from A13) and I didn’t see an option to install another update OTA.
All went well except when trying to re-lock the bootloader. After the final step to run fastboot flashing lock and then accept on the phone, the phone reboots and I get a message saying it is corrupted and cannot be booted. From here I can only access the fastboot screen.
Fortunately if I run through the installation again I can boot the phone, but as soon as I try to lock the bootloader I get stuck again.
I have tried running the lock commands the other way round and have also tried re-enabling USB debugging in developer options. Any time I go into developer options since the install the OEM unlocking box is greyed out and enabled.
The SPLs were correct between the versions of /e/ I was running/am installing and I am trying to use the official build so I’m not sure why I can’t re-lock.
Either you have got an anti-rollback situation ?? or, particularly as you say that you experimented with running lock commands backwards you have the phone in the wrong state for locking. The real hazard of bricking comes only from Android SPL errors. I have used the expression Late locker 
to describe the second as solved Installed 3.0.2 official and tried to lock bootloader - #6 by olli0371
Thanks for the tips, I do not think this is an anti-rollback issue as I can run the OS with the bootloader unlocked. I’m under the impression this would not be possible if the anti-rollback function was triggered?
The Late Locker fix did not work for me. I tried reinstalling the OS, then when I got the unlocked bootloader warning screen after the install, I immediately held down the volume down and power buttons to get into fastboot before the phone booted into the OS. From there I followed the guide, ensuring the phone did not boot past the bootloader warning. I got the same corruption message as before.
Not correct. Fairphone anti rollback is specifically triggered by locking only.Without locking rollback errors if existing are ignored.
The two dates for comparison are
- Android SPL of the build where the phone was last locked (for a new install this will be the Android SPL at time of unlocking).
- Android SPL of the build you intend to lock.
There must be “no going back” between dates.
The full rules are copied here (answered) Install /e/ on FP5 with newer Security Patches - #2 by aibd.
The fix was more complex than that. You will have to do more reading (perhaps track up to the start of that thread) if the phone is not in the correct state to lock. There are 6 or 7 late locker threads if the explanation is unclear at first pass.
Ofc from here I do not know from here the actual cause of your problem.
I’m still not having any luck with locking the bootloader but I’ll create a new thread/topic for this.
** No need, I looked through the GitLab releases and realised that v3.1.4-A15 and A14 have a security patch on 1st Sept but v3.1.4-t (which I had recently updated to) was on a patch from 5th Sept. So I am an idiot and this is a SPL issue, I will have to wait for a new patch **
I cannot see anything on the FP5 install docs about having to lock the bootloader before it reboots after the install. It seems to me that it encourages you to test the install before locking, as at the start of the Locking the Bootloader section it says:
After you have completed the installation and verified it starts up successfully, you can lock the bootloader on your FP5. This will factory reset your device again.
Just to confirm, I am looking at this documentation: Install /e/OS on a Fairphone FP5 - “FP5” and I searched for the words mentioned in some of the late locker posts:
Once you have completed the above steps and before rebooting you can lock your Bootloader.
I checked for instances of ‘before rebooting’, which returned 0, and looked through all occurrences of ‘before’ without seeing anything about this potential issue.