Hello,

Try to add the following PHP code snippet to the child theme functions.php

function custom_wc_ajax_variation_threshold( $qty, $product ) {
    return 150;
}

add_filter( 'woocommerce_ajax_variation_threshold', 'custom_wc_ajax_variation_threshold', 10, 2 );

This will increase the standard WooCommerce variations number to be loaded with AJAX from 150.

Kind Regards