Locked Track constraint issue

-Y is what you want, because the tracking bone is world aligned.  (+y runs up the length of the bone)

I'm pretty sure you have a dependency cycle that that example Hrishi.

I would need to look at your file to be sure, but if the tracking bone is targeting the widget bone.  And the widget bone is parented to all the arm chains -> which is parented to the tracking bone.......then the parent depends on the child, which depends on the parent.
This is going to cause all sorts of chaos.
If you target the CTRL bone with the constraint instead, it will work correctly.  I can't remember off the top of my head if that's what I did in the lesson, but if you started again and it's working correctly, you seem to have avoided your issue this time.

Keep up the hard work Hrishi.