If I remember correctly, on some graphics cards the change of a cursor is taken a long time when the cursor size is bigger than 16x16. And because the graphics driver is doing this with the highest priority (don’t know why they think they should do it this way) the audio threads get interrupted.
Try to use cursor sizes that are not bigger than 16x16.
And that the cursor is reset on mouse move is a bug in Cubase > 8.0.
cheers
Arne