ActiveX ComboBox not working
 

I'm using Excel 2016 and have an ActiveX ComboBox. It works fine when I insert it on a worksheet, but when I open the file each morning, the ComboBox refuses to work at all. I click on it and it doesn't respond. My workaround at the moment is to delete it and set up a new one, but obviously this is not workable ongoing. Any suggestions appreciated. TIA...