Hi, it seems like the latest nvidia drivers did cause some issues for some people on every game, including Battlefleet Gothic : Armada II (one of our QA had the same issue). Unfortunately the only fix is to revert to the previous version of the drivers until a fix from nvidia comes. Hope this helps.
It was recommended to play in window or borderless window mode for this beta because of known issues but this one is not one of them and we've never encountered it , i'll try to keep an eye out for it but we're all on a dual monitor setup so this might not be it. Do you have a new software running that you didn't have before ?