I have solved my issue with choppy and jittery cursor and editors in Cubase 10 and Nuendo 10 (and Premiere Pro).
The solution was fairly straightforward. I’d noticed that several similar threads in VI-Control, and Facebook Cubase groups had suggested trying alternative graphics cards such as an AMD Firepro. I have had x2 GeForce GTX1060 Turbo cards for the last 2 years, and had assumed that the jittery graphics were down to Windows10. But just yesterday I swapped out both of these to try a Radeon AMD WX7100 card, and WOW what a difference!!!
The WX7100 delivers very very smooth and detailed graphics, animation, rendering of everything I can throw at it. Nuendo and Cubase editors no longer pause or jitter. The cursor in the project window is now very smooth despite trying it with a template of over 2000 enabled MIDI tracks and 20 active VST tracks. Even Windows10 boots faster, and other apps such as Adobe’s Premiere Pro, After Effects are much more responsive and don’t jitter and pause for no reason.
And I’ve now freed up 3 PCIE slots on my motherboard. The GTX1060’s each require 2 slots.
I’ll report back with any updates in a week or so, but for now I’m going to stick with the Radeon WX7100 
For info, my PC’s spec is: Windows10 Pro, SuperMicro X10DAI motherboard, dual CPU (2696v3), 128GB 2133MHz RAM, x3 4k displays and x1 2k display, x2 UAD Octo cards, UAD Apollo X8, x2 2TB SSDs RAID0.