Reply To: Uncaught TypeError: Cannot read property 'src' of undefined

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 );