Thank you for letting us know that the updated graphics and Thunderbolt 3 drivers have not helped you as well and that the Display 2 HDMI port is still unstable.
I just replied to the topic starter (hofeling68) above with some additional information that may also be relevant to you.
We are still looking into the issues you had reported here. Unfortunately I have not heard back about any other possible fixes for that system yet. My apologies.
Thanks!
Josh