I have unlocked the harvester platforms and after deploying them on an ore patch and connecting the belts to the fast loaders(on both sides), none of the ores are transported back to the harvester floor. I thought I needed to upgrade them but unfortunately that did add an additional belt which also didn't work.

Just press R on the Loader to turn its direction

Oh interesting. I had to flip them around twice before they worked. Only after flipping them around it somehow started working. Odd. Thanks!