Follow the interaction
Google divides interaction latency into input delay, processing duration and presentation delay. A slow response can come from work already occupying the main thread, the event handler itself, or rendering after that handler finishes.
Start with a visitor task
Our suggested test is a real sequence: open the mobile menu, enter a search query, apply a filter and expand a product option. Try it during loading as well as after the page settles. Record the exact control that feels slow.
Investigate before disabling scripts
Use field evidence when available, then reproduce the problem in a controlled environment. Google recommends reducing unnecessary handler work and breaking up long tasks. In WordPress, investigate the responsible theme or plugin before removing dependencies blindly.
Keep a functional checklist
After a change, repeat the original journey on mobile. Check keyboard operation and focus as well as visual response. A quicker control is useful only when it still completes its task.
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