Ok, I did some investigation and it is a plugin called “Plugin Organizer” that is causing the issue. I cannot use this plugin now without the problem occurring. Actually I don’t really need the plugin anymore as my hosting has been upgraded recently. If you want to try and work out why it is causing the problem I am happy to leave it active on the staging site and give any access you need. Otherwise I am happy to call this resolved as the solution of not using the other plugin works for me.