There are several ways to trigger those twitchy Animation Transitions, here are a few.
1. Aim Down Sight while walking at normal speed - you can see that your pistol and your hands twitch once the animation ended and tries to loop. Just watch the tip of the front sight. Crouching is worse than standing.
2. Crouch and spam WASD, you'll see that your off hand ofte loses grip.
3. Using the Stance Adjust System aka ctrl+WASD makes it more apparent.