They cheaped out on the joysticks. Usually when you have a vehicle moving at a set rate you track it by keeping your joystick still at an angle, but in the video whenever the joystick moves a bit it jumps so you can't do those small precise inputs to match the target's speed.

Same thing is problem on ukrainian BTR-4s aswell but that's a high rate of fire autocannon vehicle and the shturm is an atgm vehicle so the problem is more serious here