We don't see anywhere in Gallery settings where we can specify a template. That being said, we don't use any modified templates. Everything is default or whatever the install sets. Updating to the most recent Gallery release seemed to solve the problem for about 2 page loads, then it went back to the situation where clicking the More link resulted in a single column of photos without the ability to see more photos.
This is a page that is meant to show all gallery photos from a specific user group, from newest to oldest, 24 per page. There are 4893 photos in that gallery. Opening the page by clicking the menu link shows 24 thumbnails. Clicking the More button shows a single column of 20 photos, the first of which is the last photo from the first page.
I will PM you login credentials