Remove tiny border between slide background and player?

In this screenshot, notice there is a tiny 1px border between the slide background and the player.  Oddly, it is only there on the left-hand side, and it does not appear at the top of the left-hand side (where there are shapes overlapping the background).  Can anyone let me know what I'm missing?  This is a simple gradient background, not a shape with a border stroke or anything.  Why am I seeing this thin line, and how do I get rid of it?