A common surprise: your store feels fast when you check it on your laptop, but the speed score is bad and you cannot figure out why. It is almost always the split between desktop and mobile, and mobile is the one that counts.
Desktop has more CPU, more bandwidth, and a bigger screen, so a heavy page can still feel quick. On a mid-range phone on mobile data, the same page can take three times as long. Google ranks on the mobile number, and most of your buyers are on mobile, so the mobile LCP (how long until the main content paints) is the number to fix.
The usual culprits, in rough order:
- A giant hero image served at full desktop resolution to phones. Size it for mobile and use a modern format.
- Render-blocking app scripts loading before content. Every "as seen on / reviews / popup" app adds weight; audit which ones actually earn it.
- Fonts loading late, so text pops in after a delay.
Fix the mobile LCP specifically, not the desktop one that already looks fine. When you last checked, how far apart were your desktop and mobile scores?
92 desktop, 41 mobile. Been staring at the desktop score feeling fine about nothing.
Hero image was the big one. A 1.6MB PNG sent to phones full size. Sized WebP dropped mobile LCP over a second on its own.
Then cut two popup apps I wasn't using. Auditing apps by weight opened my eyes.