I know some people may roll their eyes reading this since he's a Sixers player now. But I have to imagine Horford has some lingering injury and he's playing hurt. I mean, I can't imagine his entire game just died in one offseason.
Yes, he doesn't seem to fit well there to begin with and is simply "Embiid insurance", but I think he's still a productive player that just is out of sync lately.
I will say this though. He's not the only Sixers problem. Tobias Harris seems to disappear against great teams a lot and tonight was another example. And he's making 180M over the next 5 years. Middleton is actually worth the similar extension he signed and he's proving it. Harris, not so much.