Faced with the same problem after moving back from /e/os. There was a similar issue when I was trying to lock the bootloader on /e/os, but I was able to unlock critical clear the data and, lock critical back again and run the devices.
Just to be sure – the only way I can get my device working is to contact support and send it for repair, right?
I’m very happy for you! But I really don’t understand FairPhone’s policy: some had to pay 29€, for you it was free… While the problem comes from a bug in the system software 
If you are not able to boot (corrupted system?) AND not able to unlock the bootloader again (flag get_unlock_ability set to 0) then yes, that’s the only thing to do!
Just curious: why locking the bootloader corrupts the system that worked perfectly fine?
Perhaps, Fairphone could share files of stock images and drivers for wiping stock image.
Here is a reference to OnePlus forum
Hi everyone!
I actually had the courage to give it another go, and the flash to /e/OS succeeded
You can read through my entire process here on this separate thread: A successful attempt on flashing to /e/os on Fairphone 4
Is it now alright to disable “OEM unlocking” in the developer menu?
Hey everyone! How much time did it take FP support to respond?
I decided to call them by phone after sending my support ticket in, and that seemed to have sped things up for me
If you have the opportunity, call them when they’re open for support and explain the situation for them again. They’ll most likely see that you sent them a support ticket and have a look at it right away 
I’m in the same boat. I contacted fairphone support last week they told me that I can send it to the repair center. Still waiting for the return label. They aren’t quick…
First contacted support on June 14, I received a new phone on June 27 free of charge because the phone was 2 days old.
Lesson learned. Don’t play to much with the bootloader 
So, here is my experience with cordon and FP support:
First contact June 05, received phone at Jun 29.
It could be faster if I sent it earlier.
Free of charge, however Cordon sent me the phone with different back-lid. I had a green one with speckles. Now it’s just plain green. Also, I had a something similar to popit for extra grip. That’s weird. I hope to get the original back cover.
Hello everyone,
I read a lot of stuff in the forum about this and some seems to be lucky (get_ability=1) after installing CalyxOs or Iodé for example, but others don’t.
Does anybody have any new information about this from the Fairphone dev team? What could we do to accelerate their response and/or get their attention (all of us creating a ticket)?
I would clearly want to flash a custom rom with relockable bootloader but as this is my main phone, I will avoid this process until they have fixed this bootloader issue (that seems to be open since a long time now).
Have a nice evening
They are aware and working on a solution.
And will be open for another long time, my opinion.
Take the risk and do it.
I flashed my FP4, via my detailed instructions, now several times (iode, LeOS, FPOS, back to iode each time) and I was always able to lock it again without bricking.
It is important to do all steps very exactly! And nothing else!
@yvmuell Ok thanks
@FairphoneHulk
So an other question, let’s say I take the risk and that the “get_unlock_ability=0”, would it be possible via a simple firmware update to solve this? If not, the phone would be unlocked forever 
Ok so for your IodéOS =>
" If you get 1, everything is fine.
Then start again, beginning at Step 8)
1. remove SIM card and check that akku has at least 50%
2. eneable USB Debugging and “Allow unlock OEM” in Developer Options
3. check if adb is working and device is recognized correctly =>adb devices => ACK USB debugging on phone-screen. check box: always trust
4. adb reboot bootloader
5. check if fastboot is working and device is recognized correctly =>fastboot devices
6. fastboot flashing unlock => Acknowledge unlocking on phone (VOLUME UP + POWER) Device is doing a factory reset and reboots to system
7. start again in bootloader => switch phone off. pull out USB cable. press Volume (-) and put in USB cable in. Keep Volume (-) pressed. Phone should start in bootloader. (¹)
8. check if fastboot is working and device is recognized correctly =>fastboot devices
9. fastboot flash recovery_a iode-3.0-20220530-FP4-recovery.img
10. fastboot flash recovery_b iode-3.0-20220530-FP4-recovery.img
11. fastboot erase avb_custom_key
12. fastboot flash avb_custom_key avb_custom_key-FP4.bin
13. press VOLUME UP until see message reboot in recovery. Then POWER
14. From recovery => Factory reset => Format Data/factory reset
15. From recovery => Apply update => Apply from ADB =>adb sideload iode-3.0-20220530-FP4.zip
16. back to bootloader mode. From recovery => Advanced => reboot to bootloader
17. check if bootloader unlock ability is possible =>fastboot flashing get_unlock_ability → (bootloader) get_unlock_ability: 1 ==> if you get 1 then follow with step 18) otherwise do not lock bootloader (can brick your phone) and follow with step 19)
18. fastboot flashing lock
19. reboot system. First should see a Lineage screen doing a wipe. After a second (automatic) boot you should see the yellow boot screen and then the iode bootscreen.
20. start setup wizard
(¹) From FP Support Page:
Alternatively, you can disconnect the USB cable, turn off your Fairphone, then connect the cable and hold the volume down button. After a few seconds, you’ll see the fastboot mode"
ps: for your instructions back to stockOS, did you use the procedure given by fairphone?
if get get 0 you have a problem and a bricked phone.
if you get zero before locking bootloader again, never try to lock ist!
actual guide:
At least if the phone doesn’t boot. 
That’s imho the important rule to follow if you want to be safe.
Same problem here after trying to install Iodé.
Contacted support on June 23rd, I sent another message yesterday (June 29th) and got a reply today (June 30th) telling me that it can be repaired by shipping to France repair center for around 30 € (not under manufacturing warranty because problem happened after trying to install a third-party OS).
They told me the same thing, but the repair price ended up being 0€ anyway.