Random Trucks dump in restricted areas

See attached images

If I understood correctly, the Rules applies as "OR". That means, that if you have several overlapping towers, then "OR" rule will be applied - if anything allowed in any tower - it will be dumped

Right. Which is exactly why it should work.

As you can see, the only tower that allows ANYTHING to be dumped is the one which has an import route

ah yes, you are right, I didn't notice it in the beginning.
I also tested it and confirm the issue

And as soon as the mining designator for the Tower with "Nothing allowed to be dumped" is moved away (to different location), it starts to work as intended. For both mining Towers.

Looks like issue with overlapping designations and export/import logic.

I think this is a side effect caused by towers only setting the dumping designation restrictions to the dumping orders themselves. As a result random trucks arrive to the tower with no import routes, because that isn't restricted and dump the correct materials according to the designation.