If it's anything like RB6 Siege, it's an absolute nightmare to have an open NAT.
Your best bet is to turn your computer on the DMZ while you're playing, then turn it off when you're done.
That's the only way I can play online Siege.
unpluged my router from the wall removed enthernet cable too for couple minutes logged out of UPLAY and steam .pluged everything back loged to steam and UPLAY and get NAT Moderate and can play with friends hope that helps.