Images showing up in Post Editor, but not in Published Post

The image is there. If you view the source you can see it. If you inspect the image in your browser you can see its hidden with CSS and set to display:none;

This is the style your theme is applying.

.single .entry-content img {
    display: none;
}

You will need to override that style with your own.

.single .entry-content img {
    display: block;
}