Well that's interesting ..

As far as the OP I have only seen this when the system was under too much stress and usually relying on the inbuilt video card (meaning it is using system RAM).
Sometimes shutting down other processes helped, sometimes a simple reboot helped in these instances.
Don't know if that helps you.

As an example I tried to make a screen capture video of my cursor scrolling across the screen just now .. which it does smoothly here.
However when I played back the video screen capture it appeared to be 'jumpy'. Whether that was caused by the screen capture frame rate, the software itself, or the added load I dunno, but when I went back to the RB window the cursor moved smoothly again.
FWIW it was a file with over a dozen audio tracks with frequent edits (and many FX) & a couple MIDI tracks, so the RB load was likely >= that needed by most users.
Wish I could be more help.

Make your sound your own!
.. I do not work here, but the benefits are still awesome