Authentication issue from SharePoint Server using FQDN
If you are using a fully qualified domain name for your sharepoint site which is hosted on port 80 using domain or subdomain then you might not be able to access that site from the server itself. If you try to open the site then it will keep you prompting for user credentials again and again.
Now for that matter the problem lies in the resolution part of the domain name so you have to make any entry in backcoonectionhostnames to resolve the name to the local machine itself.
You need to run this powershell command in your server which will make an entry in your registry and you will be good to go after that :-
New-ItemProperty HKLM:\System\CurrentControlSet\Control\Lsa\MSV1_0 -Name "BackConnectionHostNames" -Value "<your domain or subdomain name without http or https>" -PropertyType multistring
To update this property in future in case you have added some more domain names
Set-ItemProperty HKLM:\System\CurrentControlSet\Control\Lsa\MSV1_0 -Name "BackConnectionHostNames" -Value "<first domain or subdomain name>","<second domain or subdomain name>" if you want to know the existing domain names in this property then retrieve by following command Get-ItemProperty -Path HKLM:\System\CurrentControlSet\Control\Lsa\MSV1_0
Do an IISRESET or application pool recycle to make apply these changes.