Let me restate your issue to make sure I understand it. You posted a link to your “Portfolio” page. When I click on any of the images on this page I go to a page that should show the individual image in full size. The images for galleries like “Yosemite” work correctly, but the images in the “MLA Gallery” show a thumbnail size image.
It looks like the single-image pages for galleries like “Yosemite” are composed with some shadowbox shortcode/plugin, but the images in the single-image pages for “MLA Gallery” are composed with [mla_gallery]. If that’s right, I think the solution is to add size=full to the [mla_gallery] shortcode. Here’s the relevant section of the MLA documentation:
Size
The Size parameter specifies the image size to use for the thumbnail display. Valid values include “thumbnail”, “medium”, “large”, “full” and any additional image size that was registered with add_image_size(). The default value is “thumbnail”. You can use “none” or “” to suppress thumbnail display and substitute the item title string for the image/icon.
The [mla_gallery] shortcode supports an additional Size value, “icon”, which shows a 60×60 pixel thumbnail for image items and an appropriate icon for non-image items such as PDF or text files.
If I’ve misunderstood the issue or that’s not the answer, having a look at the page source code would be helpful. Let me know if you need more help with this issue.