Multisite child theme files sometimes cannot load properly

Hi, I found that my multisite sometimes do not load the child theme files. For example, I have place an edited file in child theme(woocommerce/content-product.php) to show variations info on shop page.

When I check the Shop page, the edited content didn't show and i need to refresh the page several times then the edited content just show. But when I refresh the page again, the page show unedited content again. It seemed like sometimes it load from parent theme and sometimes load from child theme.

Below is the sample link for problem mention above, you can refresh several times to see the different:
http://kent.nexwee.com/shop/

How can I solve this kind of problem?