The Wall Worm Material Library Generator originally created DirectX Materials for all materials. But updates to the VMF Exporter changed the way materials are interpretted. Whenever possible, you should not use DirectX Materials.
Many DirectX shaders are crashing 3ds Max 2021, including the Wall Worm Blend Materials
There is a regression in 3ds Max 2021 that causes Max to crash when using Wall Worm's DirectX shaders for displacements.
Understanding Displacement Blend Texture Scale
This page explains one cause for displacement materials to be scaled incorrectly in Source as well as the solution. You should use bitmaps of equal dimensions in both materials controlling the Blend material.
Fix: Update to the latest NVidia drivers.
The Max viewport can freeze and become unresponsive with Nitrous in DX 11.