Installation of Gnome (Display Manager?) breaks Amazon Machine Image

Question

Launching an AMI (Amazon Machine Image) for a Ubuntu instance with installed GUI does not work. Stop/Start of the same instance works without any problems, but when you create an image of that instance and launch it, Ubuntu is stuck at startup. You cannot access the newly created instance via SSH or RDP.

Steps to reproduce:

1. Launch a fresh Ubuntu 18.04 LTS on AWS EC2
2. Make updates: sudo apt-get update & sudo apt-get upgrade
3. sudo apt install tasksel
4. sudo tasksel install ubuntu-desktop

/* Optional:

5. sudo apt install xrdp
6. sudo adduser username
7. Connect via RDP

*/

8. Stop instance and create an AMI (Amazon Machine Image)
9. List item

Launch new instance based on AMI.

What I tried:

1. Switching between sudo systemctl set-default multi-user.target <-> sudo systemctl set-default graphical.target
2. /etc/default/grub -> GRUB_CMDLINE_LINUX_DEFAULT="text"
3. /etc/gdm3/custom.conf -> WaylandEnable=false & Allow Automatic Login
4. Using LightDM instead of GDM3

Are there some settings I am missing? Any hints or suggestions I could try?