All the SquaredUp installations are done the exact same way, only this one is affcted. I compared the most important IIS settings and they are the same as in all other environments. DNS is working fine, FQDN is being resolved.
thanks for the hint. Unfortunatelly this was the first thing I checked.
It is really very odd, will wait a couple of more days and most probably reinstall afterwards, depending on whther I have time to troubleshoot this or not.
the questions is if this is worth checking when the issue affects only the server Squared Up is installed on (locally). Sorry, my bad, forgot to mention this: there is no problem accessing the web page over FQDN from all other servers/clients withing the domain,
Regards,