Steps to reproduce:

When using kernels >4.15 the system is booting into 640x480@60hz
xrandr shows no other available modelines.

Actual Results:

Linux can be used, but the resolution cannot be switched.

Expected Results:

The system should boot into the native resolution of the monitor which is 1920x1080. When executing xrandr all possible modelines should be present.
I think there is a communication error. The DisplayPort cannot read the EDID.

Hardware:

AMD Vega 56 GPU
ACER XB240H 1080x1920@144hz connected via DisplayPort
i5-6600K

Additional Information on how to temporarily fix it - add modeline manually:

I booted into a Kernel 4.15 and looked up the current working modeline for my monitor in /var/log/Xorg.0.log

then I executed following commands:
xrandr --newmode "1920x1080X"  325.08  1920 1944 1976 2056  1080 1083 1088 1098 +hsync +vsync
xrandr --addmode DisplayPort-0 1920x1080X
(xrandr --output DisplayPort-0 --mode 1920x1080X)
and the right resolution shows up.

How to boot automatically into the new modeline?
I created /usr/share/X11/xorg.conf.d/10-monitor.conf with following content:
Section "Monitor"
    Identifier "DisplayPort-0"
    Modeline "1920x1080X"  325.08  1920 1944 1976 2056  1080 1083 1088 1098 +hsync +vsync
    Option "PreferredMode" "1920x1080X"
EndSection

reboot