Phone Locked itself. Anyone else has/d this problem?

[AC Question]

I have a samsung galaxy s4. Today August 6, 2015 my phone Locked me out (No, I didn't change my password and no one else did. Nor did I forget my password.) The "lollipop" update (My phone was updated May 25, 2015) also my phone has had (still does) the letters change to squares but different forum.
So, when I got locked out of my phone, I thought of the squares, I restarted my phone. Works now but its annoying.
Has anyone else have/had this problem?