Since they seem (to me) more concerned with making the installer look nice than getting it to actually work, I now added an automatic bug report to the collection with the same error message with a little further (Edit: and probably wrong) insight to GitHub … Fastboot: Unknown error: downloading 'boot.img'...OKAY [ 0.359s]booting...FAILED (remote: bootimage: incomplete or not signed)finished. total time: 0.361s · Issue #607 · ubports/ubports-installer · GitHub .