Why does the site not work in a specific browser for a specific user?

Question

HTML

Yes... The question is strange :) A
former customer contacted me with such a message, the site does not open in his Yandex browser (as far as I understood the error with DNS). And he himself says that everything works from another browser, but he needs this particular program))
If the site has been fully tested, everything works. The problem is in his device.
But the customer shifts the blame on me, they say fix it as you want.
Ohoh .... how to answer him correctly and what to advise?

Answer 1

1. Make sure that the site actually opens in third-party services - the easiest way is to link to google page speed or tools.pingdom - they, among other things, take a screenshot of the site. And say, they say google and the whole world sees your site. All right. This is quite sobering.
2. Tell him to test the site in his browser after completely clearing the cache and in incognito mode, I once made a video just for such cases https://youtu.be/Kuh4S8zNIB8 I send it to clients so that the site is tested correctly.
3. If the client is tight, ask him to install anydesk - to access him remotely and make sure that the site is not visible from his browser even after clearing the cache and in incognito mode. Disable all extensions in general, they sometimes work in incognito. Just cut it off completely.
4. Ask him to check from the same browser, but on a different computer. You never know some particularly harmful antivirus or firewall stands as a lotion specifically for the Yandex browser and interferes with viewing.
5. Return the browser settings to default, it happens that they put a tick in the wrong place, and some sites no longer open.

Answer 2

The simplest thing is for the customer to clear the cache and cookies of the browser, you can still open it in incognito mode, which will confirm or refute my assumption.