Trucks refuse to dump very large load into very small storage.

that has only one type of material.
That way the haul trucks will contain a full load of one material only.

Enable truck overload edicts. That way the trucks can carry 234 units.
Build a loose storage I (the lowest tier, that is important). It can only hold 200 units. Set it to accept that one material. Set the mine control tower to export to it.

Trucks will get filled with material (234 units). Than they claim they have nowhere to dump it. Make sure the loose storage building is empty, reachable, properly configured etc.

Fix the problem by upgrading the loose storage. Suddenly the trucks can dump there.

I believe this is because trucks only go to a storage when they can dump all the matching contents there (234 units in this case). They ignore any storage where they could only dump part of it. But this tier 1 storage can nerver hold 234 units, even when empty, so they always ignore it.

This situation was very confusing as there was nothing wrong with the settings, the pathing and any of the other usual problems. And would I have used small trucks, it would have worked nicely. Or larger storage buildings. Or disabled the overloading edicts.

Please change the logic so that trucks can dump partial loads into a completely empty storage. Or add some feedback into the UI for this specific problem. The problem is very unintuitive when you don't know the detailed behaviour of the trucks.

Edit:
I just noticed a similar behavior: build a tier 1 storage and set it to export all ("Trucks keep empty if above 0"). Add input via belts so it is full (200 units). Assign a large truck (234 units) to it for exporting, make it exclusive. The truck just sits there and does not export anything because the storage does not have enough material to completely fill it and the truck refuses to do partial loads.

Version 3 | v0.7.6a (b466)

You should attach a save file.

bugged.save The mining tower named "bugged" near the shipyard. Loose storage (empty) for dirt is right next it, as are two trucks full of dirt. If you upgrade the dirt storage that is exported to, the trucks immediately dump their content there.

yea I've noticed this behavior seems mostly intentional to stop (or otherwise limit) trucks doing excessive small volume runs, basically a truck will do 100% of a job or 0% of that job, one exception being that a truck will get interrupted from this if a belt or other storage added or removed enough material/objects from the scheduled storage, sometimes in these instances the truck will continue with a partial transfer or it will just go and do something else

for the most part I just end up using a larger storage to let the trucks run effeciently, tier III especially for the haul trucks