I will reduce server requests, DOM size, render-blocking resources, and consequently make the site load faster and pass speed tests.
Most of the optimization is done via hand-coding internal server/website files. Caching plugins have a limit to what they can do (usually fail to exploit the maximum speed potential) and generate issues.
Typically, speed issues originate from server lack of caching and website bloat due to numerous plugins that slow down performance, non-optimized images, CSS, and JS, etc. I fix all errors originating in server/website and optimize TTFB, CSS/JS minification, reducing external calls, adding expires headers, images, etc.
12 yrs experience on Big Data and eCommerce sites (Magento, Prestashop, CS-cart, Woocommerce, OpenCart), WordPress, PHP, CSS, HTML, XML, JSON-LD, Speed optimization, Server Issues, Redirects, Mobile responsive sites, Analytics, Schema Markup, Push Notifications (Apple/Android/PC/Mac/Linux), GSC Errors: Indexation, Sitemaps, Spam Backlinks, Speed, Structured Data, Layout errors, Fast Google Indexation of Backlinks, etc.