Auto Lock Not Working Occasionally

Anyone experienced an issue in where your Blazer will not auto lock the doors when you exit the vehicle and walk away from it? I have had this happen a few times over the past few weeks and I got so used to it happening I did not pay attention for the beep or remember if I even heard one but when I come back to my vehicle later to get back in and push the button on the handle it actually locks the doors instead of unlocking them. One time I just pulled the handle without hitting the button and the door opened.