After one year I found a fix, been having the same issue and the temporary fix was using 120hz as you said, but all you have to enable is gpu scaling in the amd software and The overlapping is gone!
As you can see I have this 3 options as this:
Super res : Enabled
Gpu scaling: Enabled
Scale mode: Full screen
And now i can play stretched without that annoying line at full refresh rate.
Hope it helps!