Authentication service is not working

Do you use STAS quarantine? If so, try to deactivate it in the STAS configuration tab. 

No, It's already deactivated. Also captive portal is showing up but not responding to auth request.

In those timeframe, check the access_server.log in CLI.

Check also the current release, if not already installed. 

I have checked this log but I THINK in this timeframe no log is generated even in debug mode.

I should mention that I am not an on-site engineer and I'm receiving complaints about these issues by email. By the time I login to the firewall, the problem is solved automatically and users can login but it is an annoying issue.

I can share those logs with you in private message if you think it'll be helpful.

Hi Farshid

Please check tcpdump as well check the Authentication logs under logs Viewer Suspecting issue from AD server may be ports are getting blocked on which STAS works 

Please share the output for the below command : 

console>tcpdump 'port 6060 or 6677 

Please refer the below link for more information  : https://community.sophos.com/sophos-xg-firewall/f/recommended-reads/125318/sophos-xg-firewall-best-practice-for-stas

Thanks and Regards