A black line will appear If a Rect Light is overlapping a mesh while a Directional Light has light shaft bloom enabled. This line will originate from where the edge of the source is overlapping the mesh and extend to the edge of the Viewport. It is more visible the closer you are to it, however it flickers at distance. It will only show up at certain angles when further away.
Found in 4.20 CL# 4369336, 4.21 CL# 4541578, 4.22 CL# 4553454
A black dotted line will flicker on the screen originating from the point that the source meets the mesh, and will extend to the edge of the screen
No artifacts would appear
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-66351 in the post.