Comment 11 for bug 1799767

Ok. Crucially, this shows that you have the 1.37~18.04.2+15+1533136590.3beb971-0ubuntu1 version of shim-signed installed, which was released on October 11 to bionic-updates; superseding version 1.34.9.2 which was there previously.

Why was the shim-signed package not installed? This is the package that \EFI\UBUNTU\SHIMX64.EFI is installed from, so for it to be absent suggests something was wrong with your upgrade process. Are you sure that the \EFI\UBUNTU\SHIMX64.EFI which was installed on your EFI System Partition at the time you encountered this problem was the one from shim-signed 1.37~18.04.2+15+1533136590.3beb971-0ubuntu1 ? (E.g.: if you disable CSM again now, does the problem reappear?)