Your page takes a long time before menus, buttons, and forms start working. Visitors who click something during this window get no response — which feels like a broken site.
On WordPress
WP Rocket's "Delay JavaScript" and "Remove Unused CSS" features directly improve TTI. Enable both in the plugin settings.
On Shopify
Go to Online Store → Themes → View report (the Speed report) — Shopify shows your store's performance score and the top factors dragging it down. This tells you where to focus before making any changes.
SiteSprout scans your site, tells you which issues you actually have in plain English, and keeps watch so nothing breaks silently.
Scan your site free