This is because they've introduces new Widget panel just below clock and above notification section.
What OS think : when you try to unlock mobile, Clock widget accidentally move down vetically and back to its position and this is how you've to click sensor twice to unlock mobile.
Note : If you're using LockStar it's probably causing the issue. Try to turn it off. Else Samsung will provide some fixed to LockStar. For me issue was clock and notification section was overlapping each other which was causing this issue.
I hope Samsung will fixed this soon in India too.
