Store setup: Headless Next.js storefront on Vercel (oiloncanvas.com), Shopify checkout on custom subdomain (shop.oiloncanvas.com). Using Storefront API cartCreate mutation to generate checkoutUrl.
The issue: When the browser redirects to shop.oiloncanvas.com/cart/c/[token]?key=[key], it intermittently gets ERR_CONNECTION_TIMED_OUT. It has occurred roughly once a month since approximately April 2026, increasing in frequency — twice on May 21, 2026.
What we know:
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The Storefront API call succeeds every time with a 200 response and a valid
checkoutUrl -
The failed URLs load successfully when accessed directly in the browser seconds after the failure
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Vercel logs show no server-side errors on any checkout attempt
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The issue has occurred across multiple devices and browsers
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Shopify admin shows
shop.oiloncanvas.comas Connected, TLS provisioned, live in all regions globally -
DNS is correctly configured:
shopCNAME pointing toshops.myshopify.comverified in Namecheap
What we have ruled out: DNS misconfiguration, TLS issues, Vercel firewall rules, Next.js middleware, custom headers or redirects, server-side code errors, Shopify status page incidents, expired or malformed cart URLs.
Specific failures on May 21, 2026:
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17:24 UTC — cart token
hWNCQtiyUYkfz0ocyyrJrt9G -
21:29 UTC — cart token
hWNCQUzLjNMLkqqd1zsXgK3u
Question: Has anyone seen intermittent ERR_CONNECTION_TIMED_OUT on the /cart/c/ endpoint specifically on custom checkout subdomains? This appears to be an infrastructure-side issue on Shopify’s end. A Shopify support ticket has been submitted but I’m looking for anyone who has encountered this or found a workaround. Any Shopify engineers who can check server-side logs for those cart tokens at those timestamps would be helpful.