I have seen this on Windows 10. Sometimes if I click to drag a note or extend its length and then start dragging without delaying a little the note or note edge is no longer in the same position as the mouse cursor. I have a post about a similar issue (
https://forum.cockos.com/showthread.php?t=219737 ). I've noticed UI performance lags the longer my system is on... I can see significant response delays (5 maybe even up to 10 seconds long) if I leave the system on for a week or so. So when it's in this state, I certainly see the kind of delayed responsiveness you describe.
Maybe our issues are related?