You could try this:
1. In H1: =NOW()
This forces the sheet to recalculate when the Filter is changed and therefore triggers the code in step 3 below.
2. In I1: =COUNTA(B:B)-SUBTOTAL(3,B:B)
3. The following WorkSheet_Calculate code
The formulas in H1 and I1 could be moved elsewhere on the sheet and possibly hidden. If the I1 formula is moved to another cell, then the reference to it in the above code would also need to be changed.