Possibly trying to harvest the nodes that have crystals on them. There are certain sets of 4 nodes where 2 of them have crystals and shards and the other two have just the shards + whatever else, in which they're only harvesting those two, and as others have stated, the bot (maybe not bot) goes to the other two, stand there, and move to the next to respawn the previously used nodes. I also did this when farming topsoil nodes, crystals and seeds.