Hi,
If you use any of the smart controls (Move Vertically or Scale Vertically), Cubase creates these extra nodes.
If you click one of the node and move it up/down, the nodes are not created. You can also hold down Ctrl/Cmd modifier after the move, to make sure you are moving only in one direction (up/down) and you don’t change the time of the nodes (Constrain Direction). Or you can change the value in the Info Line while the nodes are selected. This will also not create an extra nodes.