HG633 Port Forwarding not working

Hi,

I have a HG633 through which I am trying to access a webserver. This used to work but I'm not sure when it stopped working.

I have external port 81 mapped to internal port 80, and this forwarded to my web server. I can browse to the web service on port 80 internally but when I try to browse to port 81 from outside my network I get nothing. When I use portchecker.co it says port 81 (and port 80) are closed.

I also notice I'm only on firmware version 1.15t, would a firmware upgrade help this issue?

Thanks.