I have a Samsung 2013 F series Smart TV, UA50F6700AM. This model was intended for Australia, New Zealand and Singapore. When I first purchased this model, Netflix used to work when resetting the Smart Hub to USA. However, since then, the Netflix app has updated to Version 4.00XXX. This version fails to load and switches the TV out of the Smart Hub and back to live TV. 

Yesterday, I spent a couple of hours trying to get Netflix working, and finally managed to get the Netflix app to work when my smart hub country was set to USA by doing the following:

1. Set Smart Hub to a country where Netflix is not available (like New Zealand or Australia). This will delete your existing Netflix app when the Smart Hub loads.

2. Now set the Smart Hub to a country where the Samsung App Store still has an old version of the Netflix app. Now, this used to be the United Kingdom, but this no longer works as the Netflix app in the UK has updated to version 4.00997, which no longer works with my TV. However, the Mexico Samsung App Store still uses an older version of the Netflix app, version 3.229, and this does work with my TV. Once the apps from Mexico have loaded, go to "get more apps", select "options" and set "Auto update" to "Off".

3. Now set the Smart Hub country to USA. This will delete all apps that Mexico and USA don't have in common, but Netflix will be retained and will not be updated. I still get the sever error the first time I try to load Netflix, but the second time I load Netflix, it usually works completely normally.

If you try to update Netflix Version 3.229 from the USA Samsung App Store, this will update Netflix to version 4.00511, and Netflix will no longer work. So, keep the auto update in Smart Hub Options set to "Off".

Hopes this saves someone from excess frustration.

Of course all of the above process assumes you use a DNS service like unotelly.