Secondary monitor

I use a Surface Pro 3. Through the Surface Dock I have three external monitors connected. Two in landscape and one in portrait. I use the portrait monitor for my writing. On the primary (Surface) and the landscape monitors Scrivener works just fine, but on the portrait monitor there are serious delays and problems. One example, clicking Help reveals a shadowed box, but nothing else, no menu, nothing. Move it to the landscape monitors and it works fine. But I have the portrait monitor specifically because I need overview when I write.
This is a new problem, maybe related to some upgrade in Windows, but I know I didn’t need to deal with this before.'Actually, most of my writing is done on the iOS version of Scrivener, but I like to clean up and make sure everything is connected in the larger Windows environment.