Two responses missing, but I think the pattern is indeed there.
So let’s check the other way: Who has successfully updated to A13 and had a custom ROM installed at some point in the past?
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I really can’t say but I can tell you that I followed the revert to stock guide to the point, which include flashing stock and locking the bootloader - nothing have been done after that to either lock down or up. In other words it would be in whatever state a revert to stock with locked bootloader would put it in.
You can give it a try and see if you can unlock…
Martin reflashed stock and wss fine afterwards, his bootloader was unlocked already
Although I guess you are aware: should it work be carful to relock the bootloader afterwards
Thanks mde for summarizing. Good idea, yourself. 
Just in case someone wonders: I have unlocked the bootloader and enabled USB-debigging for rooting on stock rom and never changed it back to where it orininally was. After going back to unpatched stock kernels, all of the updates went fine. So, that’s not a problem.
To me it slightly seems, that custom roms are doing something to the partitioning which was no problem for Android 12, but is for Android 13.
My initial idea was to find out, what the affected FP4’s have in common. For now it seems to be the change to a custom rom.
So, in order to make this a hit, the most urgent question to everyone affected is: does anyone have the black screen issue who did not change to a custom rom in the past?
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Allright. I recall I tried LineageOS once, but went back to full stock, locked bootloader etc.
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I had in the past LineageOs with MicroG. Then reinstalled the FP4Os. Bootloader still open.
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And you have or have not the booting issue? If you have it, can you test this?
Yes, i have the booting issue. Thats why i registered myself on this site.
I have tried to change the slots. But console says “unknown option --set-active=b”. First command works and says slot a is active.
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The command is fastboot set_active b (or a if it is already b) instead of fastboot --set-active=b if that doesn’t work try fastboot set_active other I think that should do it.
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Hi there, this won’t work with locked bootloader, as I just tried it:
Setting current slot to 'b' FAILED (remote: 'Slot Change is not allowed in Lock State
')
fastboot: error: Command failed
I guess I’ll get the UPS return label today and can send it back then…
Interesting, wherever I search also here in the forum its always as I mentioned.
Great if its just a command error, else this broken A/B fallback is even manually broken…
@anon64862762 it would be great if you could step in here and give some insights or at least take a lesson learned from those devices here to get this long known bug sorted
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hi @yvmuell !
do you mean that it’s important to lock the bootloader after the update?
is it important solely for security reasons?
No I mean locking it, can brick your FP4 due to another bug🙃
Dont boot into the system after flashing and check get unlock ability is 1…
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Same as everyone here.
I’ve got just a black screen.
I’ve installed LineageOS while waiting for Android 12 update.
I was back on FP firmware since a while, and I’ve locked my bootloader.
In recovery mode, I’ve launch “Run graphics test” and I’ve got screen
“Installing system update” then “Error!” followed by “no command” then Erasing and Installing system update.
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At least for me this analysis seems to be correct. I have not unlocked the bootloader and I have not installed a custom ROM and the update to Android 13 (C.073) went fine. I have an uptime of >25 hours and not a single reboot or any other issue that might be related to the Android system update. On the contrary, my FP4 feels better (more responsive) since the update and even the overly aggressive vibration seems to have improved.
I did, however, modify some system settings including developer options (enabled USB debugging and a few other settings) and I did disable/uninstall a few core apps (e.g. GBoard, the Google app, YouTube, …) using universal android debloater as described in this thread (with a few deviations).
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I was worried at first and didn’t do my updated.
Thanks for the conclusion USB-2, it brought me to the update.
I never modified and mine is now A13.
Not much changed but overall quite some pleasant tweeks. Essentially the same experience as user0815
Put a hart to one of the 3 posts with successful updates, if yours went through as well and you never changed your OS. Like that we don’t spam the thread more.
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Was also worried, but then i started the update on my almost-untinkered FP4 and it updated flawlessly 
Is there anyone here who had a custom ROM on their phone in the past but now managed a successful upgrade to A13?
Will there be a patch (OTA update via adb) from the Fairphone Company? Is that even possible? Or do I have to send in my FP4 brick.
I know my post has been moved to another thread.
But I want you to let you know following post on the other thread:
So I was able to test the device via an USB-C Dock. I have seen the screen and setup the device over the dock as you setup normaly over the screen.
Means Device is up an running on StockROM A13.
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