laptop crashes / freezes all the time

hi there.. I have a setup that causes a lot of crashes (sometimes every 2-4 hours).. Afterwards I need to press powerbutton as the system does not react anymore.
Here is my setup:

LAPTOP:
- DELL Precision 5550
- Ubuntu 20.04 with latest firmware

DOCK:
- DELL WD19TB
- latest firmware
- connected: DISPLAY (3440x1440x60 via displayport) and gbit ethernet