The site is unstable in some browsers, how to diagnose?

Question

Web development

The customer has problems with some functions of the site (choosing the quantity of goods and adding to the cart), it was from the phone, I determined the version of Android, found a phone with the same version, launched the site in chrome like him, there are no problems, everything works fine. He even has problems in incognito mode.

I did a survey on the site, and it really turned out that some of the functions do not work like the customer.
He updated the version of chrome. At work, some of his subordinates also have similar problems.

How to diagnose this problem?
The site is powered by CloudFlare. Actually cleared the cache, etc.

Answer 1

yes, nothing special - collect permission + user agents, lead to well-known ones (a lot of mobile browsers - forks) and hope that
there is a zoo in androids (I know about a dozen of them on the desktop), you won’t please everyone