Hey there,
Try adding below code to your theme’s functions.php file and see if it makes things any better.
add_filter('wp_get_attachment_image_attributes', function($attr) {
if (isset($attr['sizes'])) unset($attr['sizes']);
if (isset($attr['srcset'])) unset($attr['srcset']);
return $attr;
}, PHP_INT_MAX);
add_filter('wp_calculate_image_sizes', '__return_false', PHP_INT_MAX);
add_filter('wp_calculate_image_srcset', '__return_false', PHP_INT_MAX);
remove_filter('the_content', 'wp_make_content_images_responsive');
Hope it helps.