Macro problem - loops theough user defined functions not called in macro

I have been following this forum for some time but this is my first post. I am hoping that the wisdom out there can point me in the right direction to fix this problem. I have scoured the internet to no avail.

I have been compiling a workbook with many formulas, named ranges and several macros. This macro (below) has worked correctly a couple of times (step through) but usually starts to loop through the user defined functions and adds a number or rows incorrectly. I have deleted all the macros and named ranges that are not used and checked all the formulas. I am at a loss what else to do and any advice would be greatly appreciated.

Sub CopyPick()

Dim InputRngCount As Long
Dim PredictRngCount As Long
Dim InputRng As Range
Dim a As Long
Dim b As Long
Dim StartRow As Integer
Dim HoleID As String
Dim Match1 As Variant
Dim pck_import As ListObject
Dim Predict_Rec As ListObject

On Error GoTo ErrHandler

With Application
    .EnableEvents = False
    .ScreenUpdating = False
End With

Set InputRng = ActiveWorkbook.Worksheets("Recoveries Predicts").ListObjects("pck_import").DataBodyRange
PredictRngCount = ActiveWorkbook.Sheets("Recoveries Predicts").ListObjects("Predict_Recovery_Tbl").DataBodyRange.Rows.Count
InputRngCount = ActiveWorkbook.Sheets("Recoveries Predicts").ListObjects("pck_import").DataBodyRange.Rows.Count + 3 '+3 to count worksheet row number
HoleID = ActiveWorkbook.Sheets("Recoveries Predicts").Range("AP4")
Set pck_import = ActiveWorkbook.Worksheets("Recoveries Predicts").ListObjects("pck_import")
Set Predict_Rec = ActiveWorkbook.Sheets("Recoveries Predicts").ListObjects("Predict_Recovery_Tbl")

StartRow = ActiveWorkbook.Sheets("Recoveries Predicts").Range("C:C").Find(What:=HoleID, After:=ActiveWorkbook.Sheets("Recoveries Predicts").Range("C3"), LookIn:=xlValues).row
    
For a = StartRow To InputRngCount
    For b = 4 To InputRngCount
        If Cells(b, 45).Value <> Cells(a, 7).Value Then
            
            Match1 = Application.Match(Cells(a, 7).Value, Range("pck_import[Seam]"), 0)
            
            If Not IsError(Match1) Then
                    Predict_Rec.ListRows.Add (a - 3)
                    InputRngCount = InputRngCount + 1
            Else
                    pck_import.ListRows.Add (b - 3)
                    Predict_Rec.ListRows.Add (a - 2)
                    InputRngCount = InputRngCount + 2
            End If

        End If
        a = a + 1
        
    Next b
Next a


MsgBox "Data has been copied"

With Application
    .EnableEvents = True
    .ScreenUpdating = True
End With

ErrHandler:
MsgBox "Hole ID does not exist"
Exit Sub

End Sub