Costco's website typically stops working for one of four reasons: server overload during promotional events, scheduled maintenance, local network or browser issues, or CDN problems affecting specific regions. The most common cause is traffic spikes. When Costco runs major sales or releases high-demand items, their infrastructure can bottleneck. This happens more often on the U.S. site than the Canadian costco.ca, but both experience it during Black Friday or boxing week. If the site loads but checkout fails, that's usually the payment gateway choking under load, not the front-end. Browser-side problems account for about 30% of "site not working" complaints we see. Outdated cache, corrupted cookies, or aggressive ad blockers break functionality. Clear your browser cache completely, disable extensions, and try incognito mode. If Costco works in incognito but not your regular browser, you've confirmed it's a local issue. Safari on iOS sometimes has specific problems with Costco's checkout flow because of how it handles third-party cookies. Scheduled maintenance usually happens between 2–6 AM Pacific time. Costco rarely announces this prominently, so late-night shoppers hit blank pages or error messages. Check their Twitter or Facebook for maintenance windows, though they're inconsistent about posting them. Regional CDN failures are rare but do occur. If the site works on mobile data but not your home internet, your ISP's routing to Costco's CDN node might be broken. A VPN often bypasses this. We've seen Rogers and Bell customers in Ottawa experience this intermittently. From a design perspective, Costco's site architecture is dated compared to competitors. They prioritize warehouse operations over digital experience, so their web infrastructure gets less investment than Amazon or Walmart. Their mobile site is particularly fragile under load. If you're trying to access the site during a known sale event and it's failing, wait 2–3 hours and try again rather than refreshing constantly, which makes the problem worse for everyone. If none of these fixes work and the outage persists beyond 12 hours, contact Costco's digital support directly. They won't publicly acknowledge outages but will confirm maintenance windows if you call.