Sony Xperia Z2 phone - Unlock feature behaves weirdly after Android Lollipop 5.0.2 upgrade

I upgraded my Sony Xperia Z2 D6503 phone from Android 4.4.4 version to Android 5.0.2 version just 2 days back. Since then unlock screen feature started behaving weird. For instance, after locking screen by pressing power button and then trying to unlock screen by again pressing power button & double tap on my screen to wake it up (with Settings > Display > and tick the "Tap to wake up" option is ON), it automatically locks again. I need to keep unlocking it again and again till it stops unlocking automatically.

This is really pathetic and irritating. Is this Android Lollipop 5.0.2 version update issue? Please advice me on this. How can I get rid of this asap.

— modified on Apr 19, 2015, 5:34:50 AM