A dropping collection conversion rate usually traces to one of four causes: top positions filled with out-of-stock or low-stock products, a stale sort order that no longer reflects what shoppers want, seasonality shifting demand away from the products up front, or a traffic mix change sending colder visitors to the page. Work through those in that order before changing anything else.
Check inventory in the top rows first
Open the collection as a shopper and look at the first two rows. Sold-out products, products missing popular sizes, and items down to their last units all convert poorly, and if they hold your best positions they drag the whole page down. This is the most common cause and the fastest to fix: push low-stock and sold-out products down and let buyable items fill the top.
Is the sort order stale?
Manual sorts decay. The arrangement that made sense in March quietly stops matching demand by June, and nothing alerts you. Compare what sits in the top positions against what actually sells and gets clicked. Position effectiveness data makes this concrete: products converting well from poor positions are buried winners, and products holding the first row without selling are squatters.
Rule out seasonality and traffic changes
If the top rows look healthy, look outside the page. Seasonal demand shifts can sink conversion even with perfect sorting, because shoppers want different products than the ones being featured. A new ad campaign or a viral mention can flood the page with low-intent visitors and dilute the rate without anything being wrong. Check your collection view rate and traffic sources over the same window before concluding the collection itself broke.
Dynasort surfaces these diagnostics and automates the fix. Install it from the Shopify App Store or see how it works.