"One or more arguments are invalid" When UAC prompt should show

I am trying to setup a Windows 10 (1809 x64) VM in Virtualbox 6.0.4 on a Linux Mint 19.1 (x64) host. Everything seems to be working fine for a little while, then several strange things start happening in the guest OS. Most notably I am not able to run anything as administrator. When a UAC prompt should show the screen gets dark as normal, then instead of showing the UAC prompt I get an error dialog like the one attached. This occurs when trying to run anything (not just the 7-Zip installer) as admin. When this starts happening I am no longer able to open the settings app (it opens the splash screen but immediately closes). Search also stops working in Cortona/Start.
It seems that switching the graphics controller from the default (VBoxSVGA) to VBoxVGA fixes the problem, but also means that I am left with a system with many more graphical glitches. I have the latest guest additions installed and have tried reinstalling several times. Any ideas as to why this would happen or how to fix it?
Note: The issue also occurs with a Windows 10 1803 x64 guest and on a Windows 10 (1803 x64) host. The host machine is always a Dell Inspiron 15-5570 with 8th gen i5 and 16GB RAM. The Windows 10 VM has 2 virtual cores, 256MB video memory, 4GB RAM, 60GB storage. 3D and 2D acceleration are enabled.
It seems that switching the graphics controller from the default (VBoxSVGA) to VBoxVGA fixes the problem, but also means that I am left with a system with many more graphical glitches. I have the latest guest additions installed and have tried reinstalling several times. Any ideas as to why this would happen or how to fix it?
Note: The issue also occurs with a Windows 10 1803 x64 guest and on a Windows 10 (1803 x64) host. The host machine is always a Dell Inspiron 15-5570 with 8th gen i5 and 16GB RAM. The Windows 10 VM has 2 virtual cores, 256MB video memory, 4GB RAM, 60GB storage. 3D and 2D acceleration are enabled.