It could just be that he is nursing the hamstring and resting, so he isn't putting in his normal ball handling work, which has to happen at pace. That, combined with the higher levels of gameplanning and defensive intensity, probably explains the shaky ball handling, which is really the only drop off in his game at all.
I see much more up and down from Tatum, including some horrible ball handling too. There's a hype machine out there for him that Jaylen isn't part of, so that's an inconvenient narrative. While he's been awesome for a few games, he's been incredibly checked out a few games too.