Guest Additions Not Resizing

[BGB]

Bear with me if I don't describe this issue properly. I'm on a MacBook Air and prior to updating to Windows 10, when I was using Windows, VirtualBox with the Guest Additions would automatically resize the Windows screen for my wide-screen Mac. After updating to Windows 10, Windows would load but I couldn't see the full Windows desktop. That is, I could see the top (e.g., the Recycle Bin) but nothing of the bottom (e.g., the taskbar), and no ability to scroll down. In order to see the task bar, I had to enter Scaled Mode. (There is one time that it presented the full screen without Scaled Mode, but it was not in Wide-screen). What I'd like is to see the full Windows screen, in wide-screen without using "scaled mode."

I have tried re-downloading and re-installing Guest Additions several times, with no change.

I have also gone into Preference >> Display and changed "Maximum Guest Screen Size" to "hint" and entered 1900 x 1200, and restarted, but that had no effect.

I have Windows 10 Home, Version 1607, OS build 14393.321. I'm on a MacBook Air using OS Sierra 10.12. I'm using VirtualBox 5.1.6 r110634 (Qt5.5.1)

[mpack]

Try setting the display size preference to "None" or "Auto". Not "Hint".

[BGB]

The default setting is Auto, and that hasn't been working, which is why I tried "hint." But, I've also tried "none" many times.

Other suggestions? I just downloaded the newest version: 5.1.8 and re-installed Guest Additions but still not resizing to widescreen.

[socratis]

Get out of full screen, change the resolution from within the guest, reboot, change the resolution again, reboot.

Basically the idea is to force Windows to update its options. It seems ... stubbornly stuck.