Brand new, so not wear n tear, nor gunked up with solidified grease/grim/dirt/etc...
Think, or check out that the latch is adjusted properly and/or that it moves out of the way when un-latched
The coupler dome for the ball has the front (towards the TV) 'capture' the ball below the equator. Meaning that the opening is smaller than the ball
The rear of the coupler dome does NOT and is for the ball to move backwards towards the trailer and drop out of the coupler dome. The latch provides the interference below the equator of the ball
The ball also has a flat spot on the top and is to allow the ball to move backwards, away from the front of the coupler dome. Some coupler & latch setups just barely allow enough room for that flat spot to move backwards
Just some thoughts on what could be happening...first check to see if the latch gets out of the way completely and adjust if needed...but still allow it to capture the ball confidently...