Checkout failures
Payments timing out. Gateways returning errors users don’t understand. Carts that silently empty between pages. Checkout buttons that stop working for a subset of traffic and nobody can say why.
We’ve traced checkout failures to WAF rules flagging AJAX requests, Redis connection drops during peak load, PHP-FPM worker exhaustion, conflicting JavaScript between plugins, mis-configured payment gateway credentials, and browser-specific bugs that only show up in certain versions of Safari. The fix is rarely where the symptom points.