My Checkout Block shows blank or won’t render. What causes that?

Usually one of three things: a plugin that still expects the classic [woocommerce_checkout] shortcode and clashes with the Block, a JavaScript error from a conflicting plugin that halts block rendering, or a duplicate block registration after an update (Block "woocommerce/checkout" is already registered). We bisect plugins/theme, check the browser console, and pin the store to one clean rendering path.