Hello!
It sounds like you’ve made all the right decisions to try to turn off the Prev/Next buttons.
If there are only going to be 13 for each season, what you can do is add a post_count option to the shortocde. This will limit the number of posts that will be returned. Since you have the “post_per_page” option already set, you can add post_count as well, which will force one page.
[intense_custom_post post_type="galleries" taxonomy="gallery-category" template="one_image" categories="stills-season-1" order_by="title" posts_per_page="13" post_count="13" order="asc" show_author="0" show_meta="0" meta_show_comments="0" meta_show_author="0" meta_show_categories="0" meta_show_date="0" show_filter="0" filter_effects="fade, scale" image_size="square400" hover_effect="9" hover_effect_color="#000000" is_masonry="1" masonry_size="3" masonry_medium_size="3" masonry_small_size="1" masonry_extra_small_size="1"]
We’ll see if we can track down why the two pages show different results, but I think adding the post_count will do what you’re looking for, especially if you are wanting to limit the results to 13.
If this doesn’t help, please let us know.
Thanks!