dump traffic and analyze it.
something like Wireshark woul b enough 4 start.
its always better to KNOW instead of keeping guessing, just like how profilers and debuggers made for binaries/appz/libs and similary-essential diagnosis tools in medicine, math, security, management

basically if can be ANY router between you server and you router.
also aside opening ports/virtual servers/port triggering/DMZ ensure you firewall is NAT-friendly, ie NAT-essential challenges/datagramms can pass by/thru.
then start shoting down mods, starting from ACE and ACRE.