Why is my password dissapearing?

[Erica Bubbles]

I have an LG G2 and I have it set up to require a pin when I turn on the screen. However the past couple days when i turn on the screen it just goes directly to my home screen without me putting in my pin or doing anything at all. My pin reappears when i restart the phone but then dissappers again after a short period of time. Why is this happening and how do I fix it?