The button on the test page worked as there was another button (button2) on that page initiating the same pop up. This seemed to allow the button on the saved row (button1) to work.
So, I removed button2 and button1 would not work.
Next I replaced all the saved rows on my ‘home’ and ‘about’ page with a custom row with a button and this now works.
Conclusion: The on button click initiation of a pop up does not work within a shared row?