Why does one store score higher in Shopify's speed rating despite slower metrics?

[timd]

I have one client store which receives very high 80-90 scores by Shopify's Online Store Speed Rating and all of my other store's struggle with 25-35 ratings.

The speed rating page states that the scores are based on Lighthouse Performance metrics but this can't be the case because when I test 2 stores, the one that receives the high Shopify speed rating is much worse in nearly all the metrics (see table below).

The only metrics Shop 2 wins in is CLS, but the other store has an acceptable CLS so I can't imagine this would be causing the low Shopify speed score.

How could Store 2 score so much higher even though all of the metrics are so much slower?

	Shop 1	Shop 2
Shopify Speed Score	24	87
Lighthouse Performance Score	46	25
FCP	2s 400ms	6s 100ms
LCP	6s 100ms	12s 700ms
Blocking Time	680ms	9s 840ms
CLS	0.097	0
Speed Index	17s 200ms	18s 500ms

[rajvee_kadchha]

Hello Timd,

Your score is based on a weighted average of the Lighthouse performance scores for your store's home page, your product page and your collection page with the most traffic over the last 7 days.

So as it is average of all 3 pages, you need to improve it for all 3 pages to see improvement in Shopify and after making changes it takes about 7 days to get updated there.

If you have any query, or if you want to improve your store speed above 60-70, we can improve it for you. 

[timd · Accepted solution]

All 3 pages were miles better than the other store with no major changes in the last 7 days.

I contacted support about this and they've said the speed reports are inaccurate and should be disregarded. They're looking at removing them in the near future so we are focusing on Lighthouse reports.

[marvic]

Shopify's Speed Score is the most useless piece of information ever invented. It constantly averages our store at 50-60, even though all three pages tested rank 85-99 on google lighthouse / Pagespeed test when checked manually. How 3x85/3 makes 50 is a Shopify secret...