Hover over one of the images for the tooltip. When it pops up you can see the tooltip is (relatively) huge due to extra spaces inserted before and after the title. I deactivated the plugin to test and it is indeed due to Lightbox Plus.
I poked around a little more and pinpointed it to having Use WP Caption for LBP Caption toggled ON in other options. So… some phantom spacing that needs to be tracked down and eliminated for aesthetic purposes.