Polylang – browser language stops being detected

Hi,
I think this is because though polylang is showing you that the URL is getting changed, but in reality it is not. Try this:
When the plugin is installed under the cache tab of the plugin settings enable the “Purge only HTML pages” option.

Then go to your website from an incognito window and click on your language change dropdown to change the site language. Check if the site takes you to a different URL.

Now go to the plugin settings and under the “purge only HTML pages” option there is a list to see the list of URL for which the server has received requests. Check if your language URLs are there.