Hard to think of any real bad moves from Stevens. He's only made one first round pick, we'll have to wait and see how Schiereman turns out but #30 is a crap shoot in any case. His trades have been all been good to great.
One bad move may have been the Jaden Springer trade, they actually traded a decent 2nd rounder for a guy who as of right now they'd probably like to dump just to get off his money. But at the time you understood why they did it, it was to have a slightly larger contract they could use in a trade.
Maybe you could also say the Malcolm Brogdon trade. He played one year here and got hurt in the playoffs, which is an entirely foreseeable thing given his injury history. You gave up a first round pick and Nesmith who developed into a starting level SF, that's a lot for one year of Brogdon. Even if you think he helped you get Jrue, well Nesmith would have had more value in that trade than Brogdon did.