I had this very same issue and it turned out it was a plugin conflict.
Check your posts table and see what post_status is being assigned to an order. All orders were being assigned ‘wc-‘ rather than ‘wc-completed’ or ‘wc-processing’ and therefore not showing up in WooCommerce > Orders.
Having identified the plugin that was causing the issue, orders are now appearing in the orders panel, however they are being marked as ‘processing’ rather than completed annoyingly.
