Why Does It Make A Difference If A Macro is Run When Slide Show Has Started - vba

Question

Apologies if this is a basic question, but I am a newbie at VBA and have spent the past two weeks learning the language. I am trying to make a learning resource using PowerPoint.
I made a good macro which seems to work perfectly when it is run outside the slide show. (I typically just pressed F5 within my VBA Editor to see what the code was doing.) However, when I try running the macro when the slide show is running (using an action button) it does not work as intended. To be more precise it appears to stop running and not show any errors or provide reasons why the macro has stopped.
I tried doing a Google search on this topic, but could not find anything. I would be very grateful if anyone could provide any reasons or suggest any information sources as to why macros work differently when the slide show is running as opposed to not running? Are there any standard practices to ensure that the macros will work when the slide show is run?
Thank you for any comments!
EDIT 02/07/20 - responding to a comment I attach the code below and have explained what I am trying to do in comments below
Sub DataInputMacro()
'This procedure attempts to group (and do a check) of all 20 answer tiles.
Dim oSh As Shape
Dim i As Integer 'This is for the For statement
Dim iix As Integer 'This is to store the x position of the tiles.
Dim iiy As Integer 'This is to store the y position of the tiles.
For i = 1 To 20
If i = 1 Or i = 3 Or i = 5 Or i = 7 Or i = 9 Then
iix = 9
ElseIf i = 2 Or i = 4 Or i = 6 Or i = 8 Or i = 10 Then
iix = 198
ElseIf i = 11 Or i = 13 Or i = 15 Or i = 17 Or i = 19 Then
iix = 587
Else
iix = 774
End If
If i = 1 Or i = 2 Or i = 11 Or i = 12 Then
iiy = 9
ElseIf i = 3 Or i = 4 Or i = 13 Or i = 14 Then
iiy = 113
ElseIf i = 5 Or i = 6 Or i = 15 Or i = 16 Then
iiy = 218
ElseIf i = 7 Or i = 8 Or i = 17 Or i = 18 Then
iiy = 323
Else
iiy = 428
End If
ActiveWindow.Selection.Unselect 'This ensures that nothing has already been selected on the slide (which could then get grouped with the first rectangle!)
For Each oSh In ActivePresentation.Slides("DataInput").Shapes
If IsWithinRange(oSh, iix - 1, iiy - 1, iix + 179, iiy + 97) Then
'MsgBox oSh.Name & " " & oSh.Left
oSh.Select (msoFalse)
End If
Next
If ActiveWindow.Selection.ShapeRange.Count > 1 Then
With ActiveWindow.Selection.ShapeRange.Group
.Name = "GroupAnswer" & i
.Select
End With
ElseIf ActiveWindow.Selection.ShapeRange.Type = msoGroup Then
ActiveWindow.Selection.ShapeRange.Name = "GroupAnswer" & i & "a"
ElseIf ActiveWindow.Selection.ShapeRange.Count = 1 Then
MsgBox "Sorry, but there is a set up issues of your answer boxes. Either (1) one of your answer boxes does not contain a separate textbox or image or (2) there is a missing yellow rectangle! I note for point (1) the text must be placed in a separate text box to the yellow rectangle!"
End
End If
Next i
UpdateTitle 'This is a separate function that updates the title on the front slide.
CheckFor20Groups 'This is a function that checks that there are 20 groups for the rest of the program to use!
End Sub

Answer 1

Shape.Select method does not work in slide view - see remarks here: Shape.Select method (PowerPoint) - so you will have to use another method for working with your shapes - try using a variable to refer to the ShapeRange you are working with rather than ActiveWindow.Selection.ShapeRange - that way you can work with them without needing to select them.