upd. Regression was checked on //UE4/Release-4.26 CL 15973114, issue wasn't reproduced. Regression - YES
Shader compilation failure crash with DX12, Tesselation, Instanced Stereo, and Hierarchical LOD Coloration viewmode, with a shader like the following: [Image Removed]
Step 3 may or may not be required, but I didn't personally experience a crash until using that view mode.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-121129 in the post.