How to reproduce:
1. Open the attached "1275569" project
2. Open the Graph View window by going Window->05 All Combined
3. Right-click inside the Graph View window and select "New Stack"
4. Right-click inside the Graph View window and select "Create Node"->Custom->MultiPorts
5. Drag the "CustomPort" Node into the Stack Node

Expected results: The Graph View continues to be responsive
Actual results: The Graph View stops being responsive, you can only select/deselect the Stack Node and move the view around

Reproducible with: 2020.2.0a4, 2020.2.0b2
Not reproducible with: 2019.4.10f1, 2020.1.5f1, 2020.2.0a3
Could not test with: 2018.4.27f1 because the Graph View API was not yet introduced

Notes:
- Functionality that stops working:
Right-clicking to open the menu
Moving the added Nodes
Connecting the Nodes
The Toolbar becomes unresponsive
- Functionality that still works:
Panning, zooming in, and out the view inside the Graph View window
Moving the Graph View window
Selecting/deselecting the Nodes, connecting the Nodes
Dragging the multiple selections box