Comment 3 for bug 1877088

A couple of things were checked that could have causing this.
But, we for example cannot really see that 'image.postinst' is used while calling make install.
That script just seems to be incl. into deb package (as the name makes one believe).
Also "linux-update-symlinks" wasn't modified for a long time, so that doesn't seem to be the cause, too. zz-zipl postinstall just rewrites the boot loader...

I am not running into this with a normal update/upgrade - neither on bionic, not on focal.

Would you please let us know the exact steps you are using, when you run into this, so that we have a precise sequence that allows to recreate this issue?

We understood that you started with a fresh 20.04 install.
Then you probably cloned a kernel tree, like:
$ git clone https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal --branch master-next --single-branch focal-master-next
What were the next steps you did?

'Maybe' there is something bloken on your particular system - do you have a change to try on a different 20.04 installation, too?