Whenever you enter the new Gearling Firearms Dealership map, Abernathy is just slightly too far behind the counter for you to trigger a dialogue with him. So whenever you click, your character runs in the opposite direction and if given a second, so will Abernathy, making you unable to to access his wares.
One player has told me that he managed to speak with Abernathy by having someone stand directly behind him while he clicked on Gearling, forcing him to walk a few steps forward to initiate dialogue because the player could not run away. I cannot confirm this.
Spoiler: Screenshot of the Gearling Dealership show