If you can't see the chat button on chrome and IE but is working fine on firefox and Safari maybe you are getting a issue with a security rule.
The cause most likely occurs due a rule on the .htaccess file : "Header set X-Content-Type-Options nosniff" . This rule work on a different way for Chrome and IE getting a message like : Refused to execute script from [working url] because its MIME type ('text/html') is not executable, and strict MIME type checking is enabled. On Firefox , Safari and IOS work fine.
You can disable it by modifying your Apache settings or your .htaccess file, and comment the line.
#Header always set X-Content-Type-Options nosniff
To confirm you can reload the page again and check on all the browsers and see the result.