I have got this error when using the mod, i was not doing anything special on a train:

Error while running event traintunnels::on_train_changed_state (ID 23)
traintunnels/control.lua:1100: bad argument #1 of 5 to 'find' (string expected, got nil)
stack traceback:
[C]: in function 'find'
traintunnels/control.lua:1100: in function <traintunnels/control.lua:1042>

Great mod, anyway

in control.lua on line 1100 please try changing 'if find(entryStation' to 'if entryStation.valid and find(entryStation' and see if that helps