Trucks will not unload rock after finishing dumping zones.

Trucks load more material than necessary to fill available dumping zones. Once all dumping zones are filled, trucks will not redirect to available storage units and sit around doing nothing until emptied with unity.

Did the truck in question pick up the load from a storage that was assigned to export to the dumping zone?

I've seen this same issue and that was the case - because it picked up that load from the storage set to export to a particular tower for dumping, it sat there full after there was no place left to dump. That may be intended behavior to prevent breaking the export - consider a mega truck that dumps just a little to finish one square and then goes looking for anywhere to unload instead.

In this instance yes. I have had similar behaviour without the export set.

Also I tried it with a second export set to a valid storage silo and it didn't redirect.

when they load the rock the rock is tagged for that specific destination, and cannot be repurposed until manually emptied, which makes sense with the strict routes system but could be improved

one workaround can be to assign a storage as an additional destination and have that storage directly attached to the output storage

i think this is also because the tag is a fixed list of destinations, so retroactively setting new ones from the source doesnt necessarily update the trucks

destinations list being towers and storages, as opposed to specific terrain tiles

what would definitely be helpful is this tag being visible in the truck UI so you can even see why its just stuck for no reason

actually probably a good idea as well is an option to allow them to return unused material back to the storage, which would have to be paired with the yellow slider of course

To be clear, I emptied all trucks. Set a second export. Added one fill zone. When that fill zone was finished the trucks did not redirect to the second export silo.

So this is not an issue of it not being an option when the truck was loaded as I specifically tested whether having a second site available at load would work.

mmm i wonder if the new change of trucks now reserving land dumps has something to do with it

Had this happen to a truck that was assigned to a storage that had an export rule to a nearby mining tower. There was no more dumping area available, so for other reasons as well, I unassigned the truck from the storage. Game UI-wise, it's now a truck with rock that could be dumped in many other locations, and I was expecting that to happen. It didn't move and kept reporting an alert that it couldn't dump products.

I don't remember truck destinations being influenced by load origins in the past. If this is now the case, or always was, the UI should identify that the load in this truck is locked to the tower. Even then, I still think this is a bug since using unity to empty the truck shouldn't be the only solution here.