Tried it all. HDR on and off, Vulkan on and OGL. In OGL the shadows actually float in the air. AA off all the way to 4X FSAA, that is as high as I can go before the FPS starts dipping below 30 with 3 screens.
I pulled out everything last night all add ins, all lua scripts, all OSM data, all airport data, all Ortho imagery, was basically back to vanilla, and it still does it. So I am stumped.
Tried a fresh install this morning, but I lost all my joystick and panel calibrations, tried to put them back in, but was unable to control the plane. Still trying. I will let you know how I make out in a bit with a completely fresh install.
System is an i7 7700k, GTX 1080, 32gb, SSD
Edit: I just was able to get the fresh install of X-Plane 11.5 up and running to test out.
Completely fresh, no installs, nothing except an install of SkyMaxx. It does the exact same thing with the shadows. So it is not another add on or anything causing an interference.