Thanks for the response.
I've updated the sample you sent (https://dojo.telerik.com/OBawuGeZ/2) but as I said, I copied it exactly as it is in the example. So I've included some debug lines with explanations of what is happening in my local environment. I know it works in the example, but slotByElement() only returns null when I use it in my app.
Please advise, thanks,