Code not formatting strings

Attached has text in Col A in Bold, text in Col B in italics, and text in Col C as standard.

For each row, if there is text in Col A and Col D is blank, concatenate Cols A - C into Col D. That works perfectly.

Then need to find in Col D the string from Col A and make it Bold, and the string from Col B and make that Italic.

But Code throws a RunTime error 424 at that point.

Example of desired result shown in F2

Option Explicit
Dim a As Long, r As Long
Dim cl As Range, searchText As Range
Dim findText As String, findText2 As String

Sub FORMATBLEND()

    With Sheet1
    a = .Cells(.Rows.Count, "A").End(xlUp).Row
    If a < 2 Then a = 2
        
    For r = 2 To a
    
'If there is text in COl A
    If Not Cells(r, 1) Is Nothing Then
    
'If Col D is blank, concatenate Cols A - C
        If .Cells(r, 4).Value = "" Then
        .Cells(r, 4) = .Cells(r, 1).Value & " " & .Cells(r, 2).Value & " " & .Cells(r, 3).Value
    


        findText = .Cells(r, 1)
        findText2 = .Cells(r, 2)
    
            If InStr(.Cells(r, 4).Value, findText) Then
'Make Col A string Bold and Col B string Italic - throw runtime error 424
            InStr(.Cells(r, 4).Value, findText).Font.Bold = True
'Make Col B string Bold and Col B string Italic
            InStr(.Cells(r, 4).Value, findText2).Font.Italic = True
            End If
        
                
        
        End If
    
    End If
    
    Next
    
    End With
    
End Sub

All solutions, suggestions or alternatives welcome as ever.

Ochimus