Editor crashes on regenerating speed tree materials when its scaling factor is changed while it is painted on the terrain

Steps to Repro:
1. Open attached project
2. Project window > select "Conifer_Desktop"
3. Change Scale Factor and Hit apply and generate materials

Actual Result:
Editor crashes on regenerating speed tree materials when its scaling factor is changed

Environment:
Windows and Mac

Occurring with:
2018.3.0a4 (622ba39b95e4) , 2018.3.0a3, 2018.3.0a1

Working with:
2018.2.0b11