I've had TSA at BOS refuse to let me go through security when my boarding pass just had my initial and not my first name on the BP - had to go back to the desk and ask for it to be changed, makes sense I suppose, but a bit surprising the BP was printed that was in the first place.
That's a US airport thing. You often need full itinerary. Same at ORD.
I had the very same thing. Wouldn't accept my app-based check-in with full name either - it had to be on paper.