Visual artifact: problem when switching between two different custom views

Hi all,

Got myself a little issue here and I'm wondering if anyone else has seen this or has a solution:

I've got two custom screen types: one shows a tablet, and includes Notes on the lefthand side. The second type has no notes, so is typically centered in the player. It works fine throughout most of the course, then suddenly there is a tablet screen that switches to a normal screen, but the tablet is leaving a visual artifact behind in the player for the remainder of the course. (screenshot attached)

I tried re-importing the whole thing, deleting and replacing the scene where the problem appears, and then moving all the slides out of that scene into the one with the tablet so that they might run more smoothly. 

I admit that my brand new computer on which I authored this is being returned because it has some RAM and indexing issues. I'm worried that an error has been introduced because of that, but this is a very complicated course and going back to an earlier version is going to cost me several days of work. Any thoughts? 

P.S. - Possibly relevant. Prior to the artifacting issue, there was a lightbox that refused to close even though the command was properly programmed. I played around to get that to work (never seen an issue like that before) and immediately encountered this artifacting.