Flickering is occuring when using a reflection material with screen space reflection enabled. Did not start occuring until 4.19 and beyond.
Tested in: 4.23.1 CL#9631420, 4.24 P3 CL#10283392, 4.25CL#10387577
Reproduction project is attached: Open project, press play, left click and hold then move mouse left and right
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-85076 in the post.