Samsung galaxy s4- Lock doesn't show up all the time?

[Cookieli]

I just updated my phone to lollipop so I don't know if this is part of the glitches that came with the update, but this started happening yesterday. When I would go to unlock my phone, sometimes the screen lock doesn't show up. It would just show up as if there is no security lock and the ripples show up. I tried restarting my phone and that didn't work. This happens quite often. Does anyone know how to fix this?