FOR ARMA 3 (might work for others idk)
For me I fixed this problem by firstly adding the ports as u do normally on both router + firewall (Is ofc important)
secondly iam on windows 8.1
I went to control panel>system and sercurity>Windows firewall (allowed an app through Windows firewall)
arma has 3.exe applications arma3battleye,arma3launcher and IMPORTANTLY arma3server which for me was not default enabled/allowed on windows firewall
To add arma3server click change settings>allow another app search for ur arma3server.exe and add it to the lists make sure to tick both private and public boxes
this fixed problem for after i had tired everything recommended so i hope i can help you :)
oh and having to make an account to post almost put me off idea of posting my fix ;p
regards
sprinkleslol