I had similar issues. I had to update my theme’s CSS to fix the sizing of the main image. I was getting two copies of the image. One outer and one inner, and there were two sets of expansion arrows. Click on the right set and the image was loaded in the browser (no lightbox), click on the left set and the lightbox loaded as expected.
Here is an image of what I had before CSS updates: https://www.dropbox.com/s/5sqnxarahisvu8q/sampled.jpg?dl=0
I also had to put in updates to get the previous and next arrows to show properly. The previous version of the plugin had some CSS for those prev/next arrows which was changed/removed with this version. Instead, the button styles for my theme took over and I had to override those.