Lost the ability to "fastboot boot xxx.img" after installing custom OS

[oli.sax]

Continuing the discussion from [FP4] Sailfish OS - 4.5.0.24 for Fairphone 4:

@oli.sax

Actually it seems that flashing TWRP is necessary if you want to use it later…
Once SailfishOS is installed; doing fastboot boot twrp-3.7.0_11-0-FP4.img doesn’t boot to TWRP even if fastboot says ‘OK’. Instead it is stuck at “Fairphone Powered by Android screen”

Flashing twrp to both recovery afterwards and it’s working fine

Same behaviour for Ubuntu Touch, so it’s probably not SFOS-specific!

I now reflashed the stock Android image, but I noticed that I’m still not able to fastboot boot twrp.img nor fastboot boot magisk-patched-boot.img.
Using fastboot flash with the same img is working fine.

I wonder what is broken and how to debug that…

[AnotherElk]

@oli.sax

I’m still not able to fastboot boot twrp.

Is this even supposed to work?
https://twrp.me/fairphone/fairphone4.html doesn’t mention it.
https://twrp.me/fairphone/fairphone3.html does, for comparison.

[oli.sax]

@AnotherElk

Is this even supposed to work?

I don’t know if it’s supposed to work, but before I messed around it was working

[Psiko]

Not sure if this might be your issue: on Fairphone 5, I had to switch to the A slot using fastboot set_active other for TWRP to work.