So the ultimate fix we found was that we found was that in
Engine/Config/BaseScalability.ini we had accidentally set:
r.VolumetricFog.GridPixelSize=3
instead of:
r.VolumetricFog.GridPixelSize=8
Even though our [Project]/Config/DefaultScalability.ini had
r.VolumetricFog.GridSizeZ=64
Which I incorrectly identified as the same config setting.
Changing back to r.VolumetricFog.GridPixelSize=8 instantly fixed performance and corrected the black dots. I believe the black dots just to be a side effect of the GPU working too hard.
The reason that only 2 PCs out of our group had this issue is it helped us identify a bug where the settings UI incorrectly told people they were on Epic quality settings when they were not, anyone who went to epic quality (by reducing then resetting to epic quality) immediately had the bug. Only the two of us had done reinstalls that happened to correctly set us to Epic Settings.
Lesson Learned:
- I thought I had changed this once but due to a P4VS and UE4 P4 integration it reverted my change instead of submitting. So always double check the config files actually get pushed into source control.
- Really enforce your team to put scalability settings in the project level when possible instead of overriding the engine config to make config changes easy to track in one spot. But always go check for engine changes.
- Invest 15 minutes in writing your scalability settings to logs so you can quickly see if there are any differences in settings between a dev/shipping/editor build. For shipping just have it show somewhere in the UI if a special key is pressed.