I deleted my cache and also used a different browser.
But with the custom domain page (Style Guide), when you press the “next” button, the collection items stay the same and there is no “Previous” button. Whereas on the non-custom domain they change
I also had the same problem, but in my case this problem was caused by using Cloudflare Pages as a proxy between domains, because I did not send the query params to the proxy address, and the problem was solved by add the query params.