Some cooking equipment gets coated with an insulating film of grease that evaporates from the food and gets burnt on. You need a sharp probe and plenty of pressure. The moving grilles of toasters are probably not effectively earthed,, nor external chromed bezels and crumb trays. You might have to get deep inside with the probe to the actual chassis.
Thanks all, I have tried a few things and this was the answer. Getting the probe right down into the base of the toasters and pushing down quite firm did the trick while holding down the grilles at the same time as well of course - just needed three hands!