My issue is similar to this one. I removed the Windows and recovery partitions on my ultrabook to make more room for Ubuntu Linux. The EFI boot partition created by the Ubuntu installer is still there, and I found an "ubuntu" option in the EFI boot menu which starts GRUB and Ubuntu without problems, as before.
Unfortunately, this option now disappears after each boot and I get an "Operating system not found" error from my BIOS. To boot into the system again, I need to manually remove the existing "ubuntu" entry using
efibootmgr (from a live CD), which somehow helps BIOS find Ubuntu again. Running
grub-install from within Ubuntu works too. The problem is that this these hacks need to be done every time to make sure the system will be bootable next time I restart.
How can I make the option permanent? Why is it being erased? Unfortunately, ditching stupid UEFI and reinstalling the system in legacy mode is currently not an option.