As noted before that Luke Harper was recently at the WWE Performance Center in Orlando just days before WWE brought him back to TV to team with Erick Rowan in the storyline with Daniel Bryan and Roman Reigns.
The Wrestling Observer Newsletter notes that Harper being at the PC didn’t have to do with his return directly, but it did indirectly, as he had suffered a neck injury while he was out of action and away from the company. The injury was concerning, but Harper was checked out and cleared for the ring.
The Observer notes that the injury is why Harper was down in size when he did return to WWE TV.