"Booting in insecure mode" when secure boot is turned on

I have a dual boot (UEFI) Windows 10 Pro and Ubuntu 16.04. During Ubuntu install IT asked me to turn off secure boot, so I did it, using the installer. When I finished installation, I turned secure boot on again in BIOS, but I keep getting this:

Booting in insecure mode_

Every time I start my PC, before entering GRUB. I checked it on Windows and it says that secure boot is enabled, same as my BIOS. I am attaching a photo of my BIOS config:

How can I turn secure boot back on so Ubuntu will see it as enabled? Is there any way to get rid of this annoying message? Thanks in advance ;-)

I know that Dell ships their Linux systems with a variable set that disables validation: https://bugzilla.redhat.com/show_bug.cgi?id=1544794

The solution is to enable validation in that case. Perhaps this is what you're seeing? Try running:

mokutil --enable-validation