I've seen similar to this in my own game, sometimes if another Miner has selected a particular task, be it rubble or picking up ore/crystals, the other miners will leave it alone.
but I haven't had them go back and forth with 1 single item. I do know however that the miners are coded in the way of getting the nearest ore/crystal from a tool store regardless of which direction it is. Think of the area like the Radius when scanning with the Geological Center. they'll work from the Center point outwards in any direction.
This could be the explanation as to why they are running back and forth, but running back to the base before collecting the next resource shouldn't be happening if the Transporter has spaces available, I'll try some experimentation and get back to you.