1016 Error (origin DNS), but only for one user on one browser?

After some initial set-up complications, we reactivated the cloudflare proxy last night on our ecommerce site, and it has been working well all day. Until suddenly one of the staff started getting the 1016 error. I get that this error points the blame at an issue resolving the origin server, but the site was loading fine for the same person all day, and continues to load fine if they open a different browser on the same computer, or connect over wifi on their phone from the same network. It also doesn’t seem to be an issue for anyone else. So how could that be an issue with DNS to the origin server? Obviously there’s no problem resolving the nameserver to cloudflare, because it’s a cloudflare error page. And the origin server has a dedicated IP in the A record that resolves for everyone else.

What could suddenly change within a specific browser that it would trigger a 1016 error? My first thought was that they might be getting denied by a firewall on the origin server, but I’ve checked this and they are not. Also the firewall would block them from any browser/device, since it’s IP based, and they’re only getting the error in Chrome.

I’m really puzzled by this one. Obviously the staff member can carry on in a different browser, but why did this happen?

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I’d have them clear cache & cookies and try again.

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The second baffling issue in the span of a week I stumbled into the solution for.

The issue was seemingly with the WWW record on the cloudflare DNS. It was automatically imported from the previous server’s setup when the account was created, and I didn’t think anything of it. It was “flattened” to a cname in some way that I still don’t understand, so I can’t say why it was broken, just that it evidently was.

The way this manifested, the site would seem perfectly fine to anyone who loaded in to a URL without the www, but anyone who loaded with www would be redirected by cloudflare to… somewhere else? Who knows where it was supposed to go, but it produced a 1016 error. I am pretty sure there is a redirect from www configured on the server, but the client request never gets that far. And Chrome, in particular, seems to behave uniquely in the way that it memorizes the presence of a www prefix, while at the same time hiding it from you. Apparently our website had a Google business profile indexed to the www address, so people were stumbling into it.