At least that seems to be the most consistent trigger for the error. Might be LTN issues, as others have noted that it can clash.
I'm not using the wagon with LTN directly. I use LTN for regular cargo transfer, and the logistic wagon for my personal taxi/supply delivery. If I open the wagon while moving, I get the following error:
Error while running event logistic-cargo-wagon::on_gui_opened (ID 83)
Invalid selected_index - out of bounds.
stack traceback:
logistic-cargo-wagon/control.lua:571: in function <logistic-cargo-wagon/control.lua:552>
stack traceback:
[C]: in function 'add'
logistic-cargo-wagon/control.lua:571: in function <logistic-cargo-wagon/control.lua:552>
I'll probably stop using the wagons for now, since it's pretty disruptive. A fix would be great though, since the mod itself has been really helpful.