use css for resize image into mobile thumbnail

EDIT: Can you send link to that page so I can see the css?

This is a bit of a shot in the dark, as I have only done this with adding image sizes but I am sure you should be able to alter the thumbnail crop position. Are 100% the image src is incorrect and the image isn’t being cut off by css?

function setup_image_sizes() {
    set_post_thumbnail_size( 50, 50, array('center', 'center') ); 
    //Or try
    update_option( 'thumbnail_crop', array('center', 'center') );
    //I am assuming the image size is called thumbnail but it might be different if it is created in the plugin

}

add_action( 'after_setup_theme', 'setup_image_sizes' );

Reference: https://developer.wordpress.org/reference/functions/add_image_size/