The game crashes on the following sequence of events:

1) Enter the blueprint designer lab
2) Place down an obstruction and a belt pointing towards the obstruction
3) Add conveyor belts to the hotbar
4) Toggle the setting "Pick ghost if not items are available" in the interface tab of the game settings
5) Remove the rest of the conveyor belts from your inventory
6) Add underground belts to your inventory
7) Drag from the belt in front of the obstruction across the obstruction to create an underground belt (game crashes)

Here is a picture at time of crash to better illustrate what is going on: https://imgur.com/gallery/kMBoUYP
I am in the middle of dragging left to right

This is crashing for me too - but didn't use to as recently as three or four weeks ago, and doesn't always crash when placing an underground belt, just usually. Would love a fix, otherwise this mod is awesome.