Based on the color of the lines, they appear to be rows of stuck pixels continuing to display part of the drawing hand after the hand moves away. I haven't seen that symptom before but it looks like something that could be a result of videoscribe's preview play back mode, or a hardware issue.
If you attach an external monitor, does the external monitor display the same symptom?
Have you tried changing the refresh rate on your monitor to see if it affects the symptom? (Consult your mac users manual to confirm that it is ok to change that setting)
If you play the preview more than once, do the lines appear in different places?
Do the lines appear in the exported video file?
-Mike (videoscribe user)
It does sound as though it is a glitch in Videoscribe's preview feature. Maybe that's something Sparkol's programming team can look into.
If customer support does not comment in this thread, you may want to raise a support ticket.
-MIke (videoscribe user)