This problem seems to occur with Cinematic DoF (DiaphragmDOF). Licensee seems to want to use the same blur when changing resolution.
1. Create a new level.
2. Set the following post process settings to increase the blur.
4. Run the game and change the screen percentage with console commands.
(r.ScreenPercentage 100 or r.ScreenPercentage 200)
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-86012 in the post.