I have a Summary workbook with a list of Data workbook filenames.
The objective is for the Summary workbook to open the Data workbooks one at a time and have them
1) Update their data or not
2) Run Solver iterations or not
3) Save
4) Close and Return

This has been working until it doesn't work. So, the reasons are a bit hard to track down.

Right now I'm working on the "Close and Return" part.
Here is the calling Summary workbook code (simplified a bit):
Sub Updater()
Range("D2").Select
   
    Dim cell        As Range
    Dim sFile       As String
    Dim flag        As Boolean

     Application.ScreenUpdating = False
' Cells in D2:count contain path.filename.xlsm list
    For Each cell In Range("D2", Cells(Rows.Count, "D").End(xlUp)).Cells
        
         sFile = cell.Value
         Workbooks.Open sFile
         ActiveWorkbook.Close SaveChanges:=True
		 
		 Do Until WorkbookIsOpen(sFile) = False
		 Loop
        
    Next cell

     Application.ScreenUpdating = True
     Application.EnableEvents = True

End Sub
What happens is this:
After the Workbook sFile is opened and all the steps it takes are done, it returns to the code above.
I would expect it to return to ActiveWorkbook.Close .....
But, instead it returns to Workbooks.Open sFile and, it appears, there is no value for sFile at that point.
And, the next step goes to the top of the code shown here and the same/first file is opened again.

Thanks...