Playstation 4 - party chat and NAT issues

[#1]

good afternoon folks
hopefully maybe we can put our heads together and come up with a solution, i realise there are LOTS of threads on this around the web so please excuse me if it seems like a repeat, lets get the facts clear first though shall we:
ISP: Plusnet
Router: Linksys WAG354g ADSL
DMZ Enabled
PS4 Static ip assigned and set to the DMZ
PS4 reports NAT type 2
despite setting up like this i keep getting restrictive error messages when trying to use party chat, annoyingly it WORKED first time i started the console, it subsequently worked a second time, but then while trying to use a party while playing BF4 it kept failing.
i tried changing the console to DHCP and making sure UPnP was enabled but despite this it didnt work, in both cases i get a NAT type 2 result from the test but it just doesnt work, and frankly im unsure what to do, my router is fully patched up to date and so is the ps4 and bf4.
curiously i never had any issues when i had my ps3 set in the dmz. any help given would be very much appreciated, thank you

[#2]

speedtest and ping test results if anyone is interested:
yesterday evening i was getting pretty much spot on 8mb though

[#3]

I'm having the same problems actually.
I have tried all kinds of things, and I can't fix it.
Funnily enough, the Xbox Nat reports as Open, and match making and group chats work just fine.
All ports are open, I've tried using no security, wired/wireless, etc and I am still on Nat 2 on the PS4 and getting problems.
I've kinda just learned to live with it, as annoying as it is.

[#4]

trouble is on games such as a bf4 where you can have lots of friends spread accross different squads its a handy feature, better than broadcasting around the whole team annoying everyone.
anyway last night i hard rebooted my router (power off and on), i havnt done it since i disconnected the ps3 and connected the ps4 clear out the routers settings i thought. i tried a party chat while i was out of a game but a friend of mine was in and it worked, quality was good.
not stress tested it in game yet
curiously ive been told by a friend that if someone else in my party isnt setup right either they are not in a dmz or no port forwarding ill still get errors, hmmm!

[#5]

Yep that's true, and very annoying! 

[#6]

Well it seems hard rebooting it worked! anyone else having the same problem may want to setup their ps4 or console in a DMZ, set a static IP and give the router a hard reboot so it clears out any old settings