It seems the subiquity images are not affected. I have first tried the latest cosmic ubuntu-server-live image and was able to boot correctly into the system after installation. Then I have tried the old debian-installer based ubuntu-server images and was able to reproduce the issue, with the system displaying the grub prompt. This explains why I was not able to reproduce the issue before (I was using subiquity). Both on UEFI.
It seems the subiquity images are not affected. I have first tried the latest cosmic ubuntu-server-live image and was able to boot correctly into the system after installation. Then I have tried the old debian-installer based ubuntu-server images and was able to reproduce the issue, with the system displaying the grub prompt. This explains why I was not able to reproduce the issue before (I was using subiquity). Both on UEFI.