Short answer:
This is not an LTN error, and it is not a crane error. Cranes are simply larger manipulators that move entire stacks at once (and this is how they differ from "classic manipulators").
Detailed:
Your scenario is likely this:
1. Two cranes loading one wagon.
2. Mixed cargo (multiload) with a 1 locked slot via LTN’s signal.
3. Train arrives for less than a full wagon of each item — example:
4. Train is 1-2 wagons.
5. Request: 1300 copper + 2500 iron.
6. Crane swings with e.g. stack size 400.
7. After 3 swings: 1200 copper loaded.
8. 4th swing: crane commits another 400 copper → 1600 loaded, overshoot by 300.
9. Now iron won’t fit fully. During last loading attempt, crane picks iron but can’t drop all → leftovers stuck in hand → next train gets extra items.
(some scenario can happens with ash if crane hand size not exactly 250, for 251 its will be always overload and "fill" last slot ).
Just check the train schedule immediately after it leaves the loading station.
