Behavior reproduced in 4.17.2 CL 3658906, 4.18.3 CL 3832480 and 4.19.P4 CL 3873914
To run the engine with DX12 I made a shortcut of the UE4Editor.exe found at D:\Epic Games\UE_4.18\Engine\Binaries\Win64 and added -DX12 to the target
Result: Editor Crash
Expected: Flat tessellation will be applied to material
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-55127 in the post.