None of us here run with a full size window, yet none of use have ever seen this phenomenon. Only a few people are having this issue. There has to be a common denominator between the folks having this issue. We are trying to figure it out.
Does this mean not the native resolution for the monitor or, you are running the game in windowed mode for ease of accessing the desktop?
My current graphics card is a GTX 760 2G, 4096 mode. 24 inch monitor 1920x1080.
I did a test yesterday on NDisles first in native monitor mode 1920x1080, then in 1280x720. Over the Large airfields A1 and A22 starting on the ground my FPS was 30 raising into the 40's once in the air. A few miles out from A1, FPS went up to the normal 58-60. When I was a few miles out from A22 and the drones just shifted in over the field, FPS dropped into the 40s. Repeated this at the lower resolution and the spawned FPS was 50's. Once in the air 58-60 until reaching A22 at the drone shift in range.