First gallery image wrong aspect ratio

My WooCommerce thumbnail cropping setting is 1:1 in the Customer, and a 100×100 thumbnail of the product image exists, but the gallery is displaying the full-size rectangular image as the thumbnail for the first image (the rest of the images use the 100×100 thumbnails).

I tried the solution in the Wrong size first (product) thread of adding a PHP snippet:

add_filter( 'woocommerce_gallery_thumbnail_size', function( $size ) {
    return 'thumbnail';
} );

That had no effect, so I added this for good measure:

add_filter( 'woocommerce_get_image_size_gallery_thumbnail', function( $size ) {
    return array(
        'width'  => 100,
        'height' => 100,
        'crop'   => 1,
    );
} );

Still no effect. Is there something else I can try?