The real issue here is that Session made a mistake in recusing himself in the first place. The law that he cited was for criminal investigations, not counter-intelligence ones. But again, that was his call but I think he did it for another reason.
He was a sitting Senator while working as an advisor to the campaign. His only involvement with Kislayak on the campaign side was in a group meeting at a Heritage event. One subsequent meeting was a result of his role as a member of the Armed Services Committee. The reality is he misspoke during his confirmation hearing and then got tricked into saying he would recuse himself. This all happened after Flynn got canned for supposedly misleading VPOTUS on his conversation with Kislayak. Sessions knew exactly what he was doing and it was pure CYA. He should have disclosed these discussions in his confirmation hearings and not be stupid enough to walk into the trap that was laid for him. Only he knew that he had these contacts and didn't disclose them and then he recused himself to cover his tracks.