Personal.Xlsb Workbook.Activate not working

I'm trying to get a macro working in the personal workbook that I've done before, but for some reason it's not working now.

What I need is when a workbook has sufficiently loaded (or activated), for the macro in the personal xlsb to run.
At the moment, I'm putting the code in the This Workbook part of the personal xlsb and the following works fine:

Private Sub Workbook_Open
msgbox ("test")
End Sub

But if I replace Workbook_Open with Workbook_Activate, the message box doesn't pop up.

Suggestions on how to get this working please?