Having issues connecting to a particular site from behind my BM38

If I go to https://shermanpass.uwyo.edu/cp/home/displaylogin , and then
click on the link "Get Your Username and Initial Password", I get a 504
timeout error.

I have a filter exception for port 4443 in place, and one for 443, and
other sites that use https work fine.

I can get to it however if I bypass my firewall altogether, or if I
have filters unloaded, so my filter must need tweaking.