Really sounds like the Netflix application is corrupt on your box. If it's not asking to login it's failing very early on.
It would be great if you had a delete or re-install option (may be the forum team can force that somehow)
On that, I have noticed that the apps disappear if you have a network problem and the box does one of it's regular VM service updates.
At the risk of screwing other thing up you could try the following ...
1. remove the WiFi network credentials (or turn off your router's WiFi).
2. Perform a forced VM service update using the menu settings->network->connect to the vm service
3. wait for this to fail and reboot the box with the WiFi disconnected. Check if apps are present.
4. Re-establish the WiFi, reboot again and the do the connect to the vm service.