Lightroom not merging photos to Photoshop
So... I did some more troubleshooting and found out that additional images aren't opening in Photoshop ONLY when I minimize Photoshop after an edit.
So when I'm in Lightroom and merging to Photoshop for the very first time, Photoshop opens with no problem and it will continue to merge new images as long as I don't minimize Photoshop. Where the problem occurred, was after the Photoshop edit/merge, I would cmd+h to hide Photoshop. Once I did that, the next images I tried would not open.