Image is loading but not showing

I have a very weird problem and I just can’t seem to be able to find a fix.
When I load a post on my site, it’s supposed to show a main image, and any other uploaded images below it. The main image loads/shows fine, but all other images related to that post load but don’t show on the page.

The container for the images loads too, so you I can see that there’s an empty space where the images should have loaded. If I “inspect Element” I can clearly see that the image exists, and hovering over the line marks the container. I can also see that the image has loaded successfully (200). If I make any live CSS changes via the “Inspect Element”, the images pop up and shows fine.

I have a feeling it’s a CSS issue, but nothing I’ve tried seems to work. Any help is greatly appreciated.

PHP:

<?php
                    
        $arr = AuctionTheme_get_post_images(get_the_ID(), 4);
        if($arr)
        {
                      
        echo '<ul class="image-gallery">';
        foreach($arr as $image)
        {
        echo '<li><a href="'.AuctionTheme_wp_get_attachment_image($image, array(900, 700)).'" rel="image_gal1">'.wp_get_attachment_image( $image, array(130, 96) ).'</a></li>';
        }
        echo '</ul>';
                  
        }
                  
?>

CSS:

.image-gallery {
    list-style-type: none;
    overflow: hidden;
    margin: 10px 0 0;
    padding: 0;
    text-indent: 0
}

.image-gallery li {
    float: left;
    display: block;
    margin-right: 5px;
    margin-left: 0;
    min-height: 106px;
    min-width: 145px
}

.attachment-130x96 {
    max-width: 130px;
    max-height: 130px;
    width: auto;
    height: auto;
    margin: 0;
    display:block;
}

Screen Shots:

This is how the post shows when the page loads

The images shows after the slightest CSS change