I have a webserver running on Windows 2003 standard server behind a Zyxel 660HW. I configured my port-forward; I opened the port 80 on the router firewall and the server firewall. I configured my IIS 6. Everything works fine, but here is the bizarre situation; If I turned off one of my LAN computers and then turn it back-on the webserver doesn't respond any request. However, if a check my port 80 with "canyouseeme.org" I got "SUCESS" and after that my webserver starts to respond requests again.
I'm an experience IT guy but for this one I appreciate any ideas.