A1 is being closely guarded by B1. A2 sets a screen on B2 and A1 dribbles around the screen with B1 still guarding him and still within 6 foot.
In this example I have been told to drop the count when A1 goes around the screen and restart it. In the above example B2 is always within 6 foot so why would I stop the count at the screen ?

If I read your question properly B1 is always within the properties of closely guarding A1. A2 and B2, although they get in the way, do not deter B1 from his defensive (closely guarded) position. Keep the count. Have fun - -Suppref