The error always occurs as soon as I change a train in the depot to automatic and this has less than 20 fuel. I play with the mod LTN and the following error code appears:

Error while running event FuelTrainStop::on_nth_tick(1200)
real number expected got nil.
stack traceback:
FuelTrainStop/control.lua:241: in function 'AddSchedule'
FuelTrainStop/control.lua:257: in function <FuelTrainStop/control.lua:244>
stack traceback:
[C]: in function 'newindex'
__FuelTrainStop/control.lua:241: in function 'AddSchedule'
FuelTrainStop/control.lua:257: in function <FuelTrainStop/control.lua:244>

which version do you have? factorio, ltn and ATFS

Factorio: 0.17.60-2
LTN: 1.10.12
ATFS: 0.17.3

pls try the new version

Issue still exists:
Error while running event FuelTrainStop::on_nth_tick(300)
Index out of bounds.
stack traceback:
FuelTrainStop/control.lua:295: in function <FuelTrainStop/control.lua:275>
stack traceback:
[C]: in function 'newindex'
__FuelTrainStop/control.lua:295: in function <FuelTrainStop/control.lua:275>

FuelTrainStop: 0.17.7
LTN: 1.11.0
Factorio: 0.17.69