Doors and Windows - Schlage F393 entry door handleset thumpiece doesn't retract latch

What I said in my title, that's about it. The doorset is relatively new, just bought and installed in November. From the inside, the lever operates the door latch just fine. From the outside, when the thumbpiece is depressed the latch doesn't move at all. Just started yesterday. Even though the deadbolt part is separate and is working just fine, the problem with the exterior thumbpiece makes it impossible to open the door from the outside. Anyone had something like this happen before? I doubt Home Depot will allow a return at this point.

Try lubing the lever with WD 40. I did that for a friend and it works much better