What this problem looks like
Cart update failures show up as frozen quantity fields, a mini-cart that never refreshes, or products that vanish on the next page load. The underlying cart data in WooCommerce is often fine; the browser never receives the updated fragment.
Object caching plugins that cache WooCommerce sessions are a frequent cause on managed WordPress hosts. Page cache that stores the cart page HTML is another.
Symptoms that narrow the cause
If add-to-cart redirects but the cart page is empty, sessions are not persisting. If the cart page shows items but the header mini-cart is wrong, fragment AJAX or theme JavaScript is failing.
- Quantity plus and minus buttons do nothing: theme JS conflict.
- Cart clears on every page: cookie or session misconfiguration.
- Wrong totals after coupon: see coupon tutorial or tax settings.
Flush permalinks and verify page IDs
Go to Settings → Permalinks and click Save without changing anything. Then open WooCommerce → Settings → Advanced and confirm Cart and Checkout pages are set and published.
Exclude cart from every cache layer
Cart and checkout must bypass full-page cache. Also disable cart fragment caching in optimisation plugins. Some themes cache mini-cart HTML in transients; clear theme caches from the theme panel if one exists.
// wp-config.php: disable object cache for sessions during diagnosis only
define( 'WP_REDIS_DISABLED', true );Debug AJAX cart fragments
Open DevTools → Network, add a product, and watch for requests to ?wc-ajax=get_refreshed_fragments or admin-ajax.php. A 403 or 500 response often means a security plugin or mod_security rule is blocking WooCommerce AJAX.
Hosting session and cookie checks
PHP sessions must be writable on the server. Ask your host if session.save_path is misconfigured on your plan. Ensure your site forces HTTPS so the woocommerce_cart_hash cookie is not blocked as third-party or insecure.
Cookie consent plugins that block functional cookies before acceptance will break cart persistence for new visitors in the EU and UK.
When to stop DIY and hire help
Call a developer when cart issues persist on a default theme with caching disabled, when session tables grow millions of rows, or when multisite or headless setups are involved. BugShield fixes cart and session bugs on live shops without guessing.