Hi friends, I troubleshot an issue for an entire day where my Global distance field updates were taking 20ms-80ms constantly and freezing my game. It happened seemingly out of no where and I had to tear everything apart completely before I found the source of the issue was my landscape. I could never find the setting that was causing the issue, I tried to tweak all of the settings to track down the source - it was not the material, or any of the AO settings (anywhere) , or the size of my landscape, or any of its parameters - it was not until I deleted my landscape and added a new (larger) landscape in that my Global Distance field update times were fixed (now always less than 1ms, even after a stress rebuild of the level)
So yeah, good luck!