Which values were you changing specifically? I tried adding a planar reflection from the Modes tab then change the scale values in the Details panel under Planar Reflections (Normal Distortion Strength, Prefilter Roughness, Angle From Plane Fade Start, etc) but did not crash by changing these values. Can you elaborate more on what you’re doing and the resulting behavior?
Thank you for the sample video. I apologize, I was adjusting the wrong fields in my test. After further testing I was able to repro the crash and have updated UE-48038 with the steps provided.