A hypothesis is that you have this EVENT procedure in the
code module for the sheet Tracker or Test. With the name
of the procedu
Private Sub Worksheet_Change(ByVal Target As Range)
and having these lines in it:
Sheets("Tracker").Cells(iRow - 1, 4) = aNames.Count
Sheets("Tracker").Cells(iRow, 4) = bNames.Count
Sheets("Test").Cells((iRow - 1) / 2 + 4, 6) = . . .
the procedure will be initiated again whenever it hits one
of these lines. I suspect you should put the code (with a
different name) in a separate module (not a worksheet
module).

HTH,
Merjet