Debugging UC22 first boot via serial USB

I have an image for a custom model based on the reference 22-arm64 model + pi-gadget running on a Raspberry Pi 4B.

With the UC18 and UC20 versions, I could observe the first boot of my custom image via serial-to-USB using screen or tio. I could see the regular journal output without any login required. With UC22, I only get the regular login prompt, but there’s no user on the system yet.

I also have a system user assertion on a USB stick which was auto-imported on UC18/20 versions of my image. With UC22, this does not get imported – at least I cannot login with the known credentials. If I understand the docs for auto-importing a system user assertion correctly, the import might take several minutes when I attempt this during first boot – but if there’s an issue during first boot, UC might never get to the point where it auto-imports an assertion?

@ogra Do you have any pointers where I might start? My gadget adds nogetty fbcon=rotate:1 to cmdline.txt and disable_splash=1 + disable_fw_kms_setup=1 to config.txt, rest is snap default config, connections and a custom splash logo (works flawlessly).