Can't See Web-Greeter but GTK-Greeter

[luxploit-old]

OS: Ubuntu Mate 16.04.6
Kernel: 4.15.0
Method to install: OBS Repos

I'm Running a VirtualBox in which I've Installed Ubuntu Mate 16.04.6 LTS. By Default it comes with the ugly GTK-Greeter. So I installed the lightdm-webkit2-greeter packages via the OBS repos. And It Worked
fine, until i changed the VirtualBox Video Ram from 16mb to 128mb and Enabled 3D. After That i was unable to see the Greeter, only a Black Screen.

Here is a Screenshot of sudo systemctl status lightdm.service: https://i.imgur.com/3euvG7W.png

EDIT: It Seems To Work Fine without 3D enabled, though still having 128mb of VRAM