unfortunately I have also trouble with my XPS 9570 since some months.
I hope that maybe someone can give me the right hint.
If the notebook is started or woken-up with external display attached, the external screen is sometimes blank (probably no valid signal), sometimes all blue (the default wallpaper color) with glitches at the top. The mouse and keyboard (system?) are frozen. If unplugging the display again the systems sometimes recover after a while. This also sometimes happen if the display cable is plugged in during operation but not that often.Without external monitor the notebook operates fine.
As there are many threads reporting similar problems with 9560 or 9570 it is probably not a hardware failure but bios driver issue.
Setup: XPS 9570 BMTDHR2, BIOS version 1.16.2 FHD display connected via HDMI to a Samsung LU32J590UQUXEN display Windows 10 Home, 10.0.18363 no TB-Docking station
What I have tried without success:
- installing latest drivers with dell update - different hardware: displays, different cables, type-c usb hub with hdmi out - installing latest intel drivers - reinstalling windows via dell cloud recovery
with the blank reinstalled windows it does not occur that often, but as the notebook sometimes freezes completely and all unsaved data is lost this is not a satisfying solution.