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.