I would guess it is a resource issue when the screen is updated and the PC is doing so much besides updating the screen that it takes time between blacking out the old and showing the new.
You could look at the resources your PC has, compare it with what Win 10 needs and the maximum you can fit (memory and processor speed maybe) and see if there's room for upgrading.
Maybe looking at the task manager and see what it is trying to use might give a clue. Perhaps some things can be closed down.