Second half VBA macro runs 3x faster if i don't run the first part before - excel

Question

I have two macros:
Macro 1: copy-paste a large worksheet into the same workbook (basically myWorksheet.copy after:=lastWorksheet)
Macro 2: Iterate through data in new worksheet to unmerge any merged cells. Then set the value of all cells in each MergeArea to the value of the original merged cell.
Both macros run as they should.
The problem is the runtime. If I run Macro 1 and Macro 2 in the same 'session' (the way it has to be) Macro 2 has a runtime of roughly 250s.
If I run Macro 1, then restart Excel and run Macro 2, Macro 2 takes only 1/3 of the time (~70s).
I tried clearing the clipboard after running Macro 1 but it does nothing. Otherwise I'm out of ideas.
Macro 1:
Sub copySheet()
Dim ws As Worksheet
Application.DisplayAlerts = False
Set ws = ThisWorkbook.Worksheets("BigData")
ws.Copy After:=ThisWorkbook.Worksheets("BigData")
Application.DisplayAlerts = True
End Sub
Macro 2:
Sub unmergeCells()
Dim ws As Worksheet
Dim szArr() As Integer
Dim i%, k%, j%, col%
Dim strt&
'First row
Const fr% = 9
'First column
Const fc% = 12
'Last column
Const lc% = 135
'Last row
Const lr% = 1196
Application.ScreenUpdating = False
Application.Calculation = xlCalculationManual
Set ws = ThisWorkbook.Worksheets("BigData (2)")
strt = VBA.Timer
With ws
For col = fc To lc
'Some columns only have to be unmerged without changing any values
If IsNumeric(.Cells(fr - 1, col)) Then
.Range(.Cells(fr, col), .Cells(lr, col)).UnMerge
GoTo Skip_Ahead
End If
i = fr
k = 0
Do While i <= lr
ReDim Preserve szArr(k)
szArr(k) = i
i = i + .Cells(i, col).MergeArea.Cells.Count
k = k + 1
Loop
.Range(.Cells(fr, col), .Cells(lr, col)).UnMerge
For i = 0 To UBound(szArr) - 1
For j = szArr(i) + 1 To szArr(i + 1) - 1
.Cells(j, col) = "'" & .Cells(szArr(i), col)
Next j
Next i
Skip_Ahead:
Debug.Print col & ": " & Timer - strt
Next col
End With
Application.ScreenUpdating = True
Application.Calculation = xlCalculationAutomatic
End Sub