Array returning all zeros

In the code some issues found like lastRow1 = Sheets("DeSL_CP").Range("A" & Rows.Count).End(xlUp).Row preferred to be based on Col B. also think starting value for the For loops should be 1 instead of 7 and 2 (depending on Option Base). ResultArray could be populated directly from BaselineEnd(j, 1). Finally ResultArray was solved with Range("M7").Resize(UBound(resultArray), 1).Value = resultArray. The Consolidated final code:

    Option Base 1
Sub test()
Sheets("Summary").Select
Dim lastRow As Long, lastRow1 As Long
lastRow = Sheets("Summary").Range("A" & Rows.Count).End(xlUp).Row
lastRow1 = Sheets("DeSL_CP").Range("B" & Rows.Count).End(xlUp).Row
lastRow1 = lastRow1 - 1


Dim BaselineEnd As Variant, ActivityCode As Variant, ProductIDDeSL As Variant, Licensed As Variant, ProductIDSumm As Variant
BaselineEnd = ThisWorkbook.Worksheets("DeSL_CP").Range("P2:P" & lastRow1).Value
ActivityCode = ThisWorkbook.Worksheets("DeSL_CP").Range("K2:K" & lastRow1).Value
ProductIDDeSL = ThisWorkbook.Worksheets("DeSL_CP").Range("B2:B" & lastRow1).Value
Licensed = ThisWorkbook.Worksheets("Summary").Range("AK7:AK" & lastRow).Value
ProductIDSumm = ThisWorkbook.Worksheets("Summary").Range("A7:A" & lastRow).Value

Dim resultArray() As Date
ReDim resultArray(lastRow - 7 + 1, 1)
Dim i As Long, j As Long

With ThisWorkbook.Worksheets("Summary")
For i = 1 To UBound(ProductIDSumm)
    For j = 1 To UBound(ProductIDDeSL)
    'If Not Sheets("DeSL_CP").Rows(j).Hidden Then
    If ProductIDSumm(i, 1) = ProductIDDeSL(j, 1) Then
        If Licensed(i, 1) = "Unlicensed" Then
            If ActivityCode(j, 1) = "AA0001" Then
            resultArray(i, 1) = BaselineEnd(j, 1)
            Exit For
            End If
        Else
            If ActivityCode(j, 1) = "A0003" Then
            resultArray(i, 1) = BaselineEnd(j, 1)
            Exit For
            End If
        End If
    End If
    'End If
    Next j
Next i

Range("M7").Resize(UBound(resultArray), 1).Value = resultArray
End With
End Sub

I tried simply with out any array and found working correctly

Sub test2()
Sheets("Summary").Select
Dim lastRow As Long, lastRow1 As Long
Dim i, j As Long, Found As Boolean
lastRow = Range("A" & Rows.Count).End(xlUp).Row
lastRow1 = Sheets("DeSL_CP").Range("B" & Rows.Count).End(xlUp).Row
lastRow1 = lastRow1


Dim BaselineEnd As Variant, ActivityCode As Variant, ProductIDDeSL As Variant, Licensed As Variant, ProductIDSumm As Variant

For i = 7 To lastRow
Found = False
ProductIDSumm = ThisWorkbook.Worksheets("Summary").Cells(i, 1).Value
Licensed = ThisWorkbook.Worksheets("Summary").Cells(i, 37).Value
If ProductIDSumm <> "" Then
    For j = 2 To lastRow1
    ProductIDDeSL = ThisWorkbook.Worksheets("DeSL_CP").Cells(j, 2).Value    'Col B
    ActivityCode = ThisWorkbook.Worksheets("DeSL_CP").Cells(j, 11).Value   'Col K
    BaselineEnd = ThisWorkbook.Worksheets("DeSL_CP").Cells(j, 16).Value    ' Col P
    If ProductIDDeSL <> "" Then              ' to skip blank rows
    If ProductIDSumm = ProductIDDeSL Then
        If Licensed = "Unlicensed" Then
            If ActivityCode = "AA0001" Then
            Found = True
            Exit For
            End If
        Else
            If ActivityCode = "A0003" Then
            Found = True
            Exit For
            End If
        End If
    End If
    End If
    Next j
ThisWorkbook.Worksheets("Summary").Cells(i, 13).Value = IIf(Found, BaselineEnd, "Not Found")
End If
Next i

Edit: Since You are supposedly in possession of a large data and having processing time problem. merely on curiosity I am adding the find method solution as third option

Sub test3()
Sheets("Summary").Select
Dim lastRow As Long, lastRow1 As Long
Dim i, j As Long, Found As Boolean
lastRow = Sheets("Summary").Range("A" & Rows.Count).End(xlUp).Row
lastRow1 = Sheets("DeSL_CP").Range("B" & Rows.Count).End(xlUp).Row
lastRow1 = lastRow1
Dim RngIDsm, RngIDde, Cl, Cl2 As Range
Set RngIDsm = Sheets("Summary").Range("A7:A" & lastRow)
Set RngIDde = Sheets("DeSL_CP").Range("B2:B" & lastRow1)
Dim BaselineEnd As Variant, ActivityCode As Variant, ProductIDDeSL As Variant, Licensed As Variant, ProductIDSumm As Variant

For Each Cl In RngIDsm
Found = False
ProductIDSumm = Cl.Value
Licensed = Cl.Offset(, 36).Value
    With RngIDde
    Set Cl2 = .Find(ProductIDSumm, LookIn:=xlValues)
    If Not Cl2 Is Nothing Then
        firstAddress = Cl2.Address
        Do
        ActivityCode = Cl2.Offset(, 9).Value  'Col K
            If Licensed = "Unlicensed" Then
                If ActivityCode = "AA0001" Then
                BaselineEnd = Cl2.Offset(, 14).Value
                Found = True
                Exit Do
                End If
            Else
                If ActivityCode = "A0003" Then
                BaselineEnd = Cl2.Offset(, 14).Value   
                Found = True
                Exit Do
                End If
            End If
        Set Cl2 = .FindNext(Cl2)
        Loop While Not Cl2 Is Nothing And Cl2.Address <> firstAddress
    End If
    End With
Cl.Offset(, 12).Value = IIf(Found, BaselineEnd, "Not Found")
Next Cl
End Sub