Just installed N8.3.20 and now, when a project first opens, there is a narrow vertical row of waveform graphics and an additional (inactive) vertical scrollbar to the right of the active vertical scrollbar on the right edge of the Project window.
It looks to me like the way the Project would be initially drawn before the waveforms are re-drawn in accordance with the Track heights.
If the right edge of the Project window is moved slightly to the left the problem goes away.
Seems like something is not being cleared properly.
This only happened with N8.3.20 - I noticed that Windows Scaling was set to 125% although no scaling was actually happening. After setting scaling back to 100% and then re-selecting 125% the glitch went away. I guess something to do with a recent upgrade from W7 to W10.