I have a UN40EH5300F.
For several months, WiFi connection has been fine.
I started have problems with Hulu & Amazon Inst. Video. After forcing a software update, the problems when away then returned. When I tried to access Samsung Apps folder I got:
Network Interference occurred
Please try again later
Like you, I have all of strong connection with other devices. I made sure no updates were waiting--including exiting the Smart Hub first before asking for updates.
I changed the DNS to 126.96.36.199 and then 188.8.131.52
During this time problems with Hulu and AIV persisted, but YouTube and Netflix worked.
When I came back this evening, and it took a while for the Smart Hub to load. Then (1) YouTube and a couple of other apps I don't remember adding were gone. (2) Netflix no longer opens--just connecting wheel, and (3) problems with Samsung Apps folder, Hulu, and AIV remain the same.
I guess it's time to buy an HDMI cable.