External Monitor turns randomly off.

Good morning,

i have a problem with my 2 external monitors on my XPS 7590 with i7 9750H. 

I have it connected with 2 external monitors as dual screen setup (Laptop screen turned off). One monitor is connected via the HDMI port and the other one via USB-C with a USB-C to HDMI cable. 

I have following problem: The monitor i have connected via the in-built HDMI port turns off and states that no HDMI input is received when i browse in ithe internet. This happens with different websites and with some games I start. The only solution is turning off my Laptop and restart again. I tried several solutions already, like BIOS update, several driver updates, different HDMI cables etc. I guess it is not a problem of the monitor because when i plug the whole setup on another Laptop, it works just fine. 

I hope you can help me finding a solution. Thanks in advance!