When enabling Forward Shading in a project while using the Lumen Global Illumination system, the shadows in the viewport begin to flicker and occassionally entire meshes may appear black. The lighting also seems overblown as well.
I tested this with Forward Shading disabled and did not encounter the issue. I also tested with Forward Shading enabled, but Lumen disabled and did not encounter the issue either, so it seems to be the combination of both rendering settings.
The shadows start to flicker
Forward Shading would not causing Flickering when using the Lumen GI system
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-116639 in the post.