This is a problem that has persisted for several versions (since Cubase 7 or 7.5 I think). It worked nice previously.
Due to the way the events are drawn when they are dragged around (transparency effect), they are very hard to see if the editors background colour is light. We are being forced to use dark (and depressing) colours for the editors and I really would love if that wasn't the case.
1 - Open the appearance settings and on the Colors -> Editors option set the Work Area Color to white.
2 - Create an instrument or MIDI part and open the note editor.
3 - Draw some note events, and then drag them around with the mouse.
Result: Dragged notes are completely invisible.
Also, the tip with info about the events being dragged looks ugly. It looked much better in the old versions too.