I'll try my best because English is not my mother tongue. I'm Brazilian. I used the DMZ and static IP method on my ps4 and I was able to play without being disconnected. Use google to see how to change the ip from ps4 to static, then just go into your router and go to the DMZ tab and put the ip there and go! enjoy the game!
'The server is currently unavailable. Please try again later' have been haunting me since release, even after the patch. But after setting up the DMZ, I've played for hours tonight, and the servers worked without issues.