I think this is easy to reproduce, just place down some connected locomotives with locomotives in the same train pointed in different directions, the first one you place that is in a different direction will crash the game with the following exception:
"The mod Multiple Unit Train Control (1.0.3) caused a non-recoverable error.
Please report this error to the mod developer"
"
Error while running event MultipleUnitTrainControl::on_tick (ID 0)
Robot256Lib/script/carriage_replacement.lua:142: attempt to index field 'schedule' (a nil value)
stack traceback:
Robot256Lib/script/carriage_replacement.lua:142: in function 'replaceCarriage'
MultipleUnitTrainControl/control.lua:164: in function 'ProcessReplacement'
MultipleUnitTrainControl/control.lua:275: in function 'ProcessTrain'
MultipleUnitTrainControl/control.lua:377: in function 'ProcessTrainQueue'
MultipleUnitTrainControl/control.lua:405 in function
<MultipleUnitTrainControl/control.lua:402>
"
