enthropy6203 Problem was, that i originally was to lazy to download the platform tools and tried to use an outdated fastboot version by deleting the version check in flash-all.sh.
Thanks for reporting back! This information is useful.
Honestly it's lucky the device wasn't bricked.
Everybody, please be careful out there! I think it was around a year ago that a forum user permanently bricked a Pixel by forcing the wrong image onto it. A bootloader-unlocked Pixel is a vulnerable Pixel.
New versions are released because they fix bugs. Scripts contain version checks because the old versions do things wrong. It's good this particular story has a happy ending, but they don't all...