I found a Windows anti malware process was causing my X-Plane
frame rate to drop to between 3-6 FPS.
This on a computer with an i7 8700K, a GTX 1080Ti and 32 GB of RAM.
In this video I show how to prevent that from happening to you. The short of it is you can turn of Windows Defender or add an exception for any app that may be causing this.