I have the exact same problem. I'm running a UHD monitor at 3840x2160. It started a few days ago, then disappeared after a manual windows update. It returned the next day. After a display driver update from Nvidia it went way for a day, then returned.
It effects Word and Outlook, but not Powerpoint or Excel.
It also effects a drawing program I use called Corel Designer, which is really annoying.
It's clearly a bug linked to display driver problems and the cursor files a program selects.
If anyone finds a permanent solution please post it here!
I'm sorry you're also having this problem. I agree that I see the issue in Outlook and Word. I too have never noticed it in Excel. It does appear in the drawing program I use called paint.net.
[This appears on two systems I use daily. One is an i5, one an i7. Both use higher end nVidia GTX cards, 3840x2160 at 150% scaling, MS Office365, optical mice with the default MS driver, and updated Windows 10. For what it's worth...]