I added a BBOX expression to an object (object B) and it's referencing another object (object A) I have since changed the depth / scale of (object A) since that change of depth / scale (object A) does not conform to (object B) bounding box; I was hoping it would adjust automatically ?

It is hard to say without seeing an example scene of the problem. Try moving the timeline to another frame?

There is only one additional node after the node being referenced. Moving the time line didn't work

Not quite sure how are you attempting to match the bounds, but I attached one way (probably not the best one) to match obj A (sphere) to obj B (cube) bounds. It takes into consideration sop level bbox and multiplies it with obj level scale and sx,sy,sz. It also matches the position of obj A to the centroid of obj B.

el_diablo, injecting a little math into the expression seems to have worked I'm still not satisfied even though it worked