Global $product cause Oxygen does not refresh CSS

The issue is related to the custom PHP functions being used the Repeaters in WooCommerce templates. Within the custom functions, after you call global $product, you need to wrap the rest of the function in an if($product) { ...do stuff here } statement. This will prevent the AJAX errors.

global $product;
if($product) { ...do stuff here }

Also do not use Global $product on single product template. Instead use:

$product = wc_get_product( get_the_ID() );