Excel automatically changes charts from landscape to portrait view

I have a number of charts that have their own location (not within a worksheet) and for some reason they have reverted to a portrait orientation even though I created and saved them in landscape orientation. When checking page layout orientation, it is greyed out and landscape is still selected. Some other times when the orientation automatically changes to portrait, I check the orientation and it is no longer greyed out yet landscape is still selected; I'm able to fix the chart by selecting portrait view and then landscape view again, after which the chart returns to normal. After closing and reopening the file, the charts revert back to landscape mode. I find it most annoying having to close and reopening files or constantly having to perform the page orientation switch because the charts keep changing orientation automatically.

Has anyone experienced this or can anyone offer any suggestions? I'm running windows 8 with Office 365.

I encountered this issue back in 2014 for the first time. It occurred in a virtual environment (VDI session) when you would time out of the session. Upon re-entering, all chart pages had changed their orientation from Landscape to Portrait. The option to change the page orientation would be unavailable (grayed out), so the only recourse was to close and reopen. If there were unsaved changes, they would be lost.

To help remedy the situation, I wrote a macro that changes all chart sheets (in the selected workbook) from Portrait to Landscape orientation. It's not a solution, or even an explanation as to why the orientation changes, but it can help, if you have unsaved changes that you'd rather not lose.

Here is the code:
Sub SetChartsLandscape()
'******************************************************************************
'* This macro loops thru all "chart sheets" in a workbook, and sets the
'* page orientation from portrait to landscape.
'******************************************************************************
Dim i As Integer
Dim Msg3 As String, Resp3 As String
Const MacroName As String = "SetChartsLandscape"
'* verify before starting
Msg3 = "Do you wish to set all chart sheets to landscape orientation? "
Resp3 = MsgBox(Msg3, vbYesNo + vbQuestion, MacroName)
If Resp3 = vbNo Then Exit Sub
With Application
.ScreenUpdating = False
.PrintCommunication = False
For i = 1 To Sheets.Count
If Sheets(i).Type = 3 Then
With ActiveChart.PageSetup
If .Orientation = xlPortrait Then .Orientation = xlLandscape
End With
End If
Next i
.ScreenUpdating = True
.PrintCommunication = True
End With
MsgBox "Process Complete. ", vbOKOnly, MacroName
End Sub