Reproduction steps:

1. Open "MinimalRepro.zip" project
2. "Octane" -> "Settings" -> "Load Octane"
3. Close the "Octane" window
4. "Octane" -> "Viewport"
5. Dock the "Viewport" somewhere (e.g. Next to the Game Window)
6. "Alt" + "Right Mouse Button" drag the "PBR Viewport"

Expected Result: The Viewport rescales to the users' mouse position
Actual Result: The Editor crashes

Reproduced with: 2017.3.0a7, 2017.2.0b10, 2017.1.1f1

Note:
After launching the project click Install on the Octane pop-up (Might pop-up 3 times)
Asset only works with 2017.1+