You have activated the extra subscription for 4screens and UHD haven't you? £8.49 per month
Also to stream netflix 4k your equipment needs to be HDCP2.2 compliant Are your TV and ROKU box HDCP2.2 especially the TV my panny only has 2 ports dedicated to HDCP2.2 that's hdmi 1 and 2 so make sure everything is connected properly. If your not connected to hdcp2.2 then 4k content might not even show let alone play.
did a quick search on google lots of people having problems with the roku box only outputting 1080 so it might be worth you having a look.
does it not have a netflix dedicated app inbuilt like the panasonics do? it's actually rather good but ultimately on 4k you still get some interpolation due to the compression. it affects some programs more than others. I'm really keen to try a 4k blu ray but really not keen on the price of the players.
Thanks for the reply again. I am pretty sure the Sammy 9000 is 2.2 compliant, and I have got the Netflix £8.99 account which includes 4K, but there is no way on the Roku box settings to enable 4K only 1080 under tv res.
Will try the inbuilt player on the Tv and see if that is any different.
Mark