Hello everyone !
I also have the same problem with a 34 '' Samsung S34J55X screen and the new surface dock 2.
I updated the dock2 drivers but it doesn't change anything.
My screen works well when I plug it directly into my ebook2 surface (with HDMI / USB-C adapter).
I hesitate to buy the microsoft HDMI / USB-C adapter because the price is high and I'm afraid it won't change anything.
I'm very disappointed with this purchase. I'm thinking of going back to dock1 and trying to get a refund..