I've created a Python toolbox using the Python toolbox template. I've configured Visual Studio 2017 to recognize .pyt files as Python files. I've used the instructions here to set up debugging for my Python toolbox.
To debug, I attach the Visual Studio debugger to the ArcGISPro.exe process as Python code, as shown in the screen shot below. I've set breakpoints in my code. However, when I run a tool from the toolbox, none of the breakpoints are hit.

Does anyone have any insight as to why I can't debug?
Visual Studio 2017
ArcGIS Pro 2.2
Python 3.6