Dimmer overheating 289 degrees Celsius

Hi everyone, I am new to this group so any help is appreciated. So I recently purchased a bunch (8 in total) of new Shelly dimmers 2 to the UK. I wired them up with no neutral and my bulbs are 100% dimmable and above 10watts. They are LED cool white and each bulb is approx 3.5W. These worked perfect before I installed the Shelly. So, here is the problem on two of my switches it works perfect, on another switch the Shelly overheated! Really bad! The website says it has a automatic cut off when temperatures get too high? What cut off is this 300degrees Celsius?! I then went to proceed to change this Shelly for the second one in the same box exactly the same thing happened. (Makes me believe faulty batch maybe). What is baffling me is why is it working on some rooms and not in others, and why did the cut off switch for the temperature not kick in? My devices got so hot the plastic began to melt!! I did not get any notifications in the app or anything only the GUI, I only realised it was hot as the GUI comes up with the temperature once it is above 200degrees C. This can not be safe to use? I know it will be in a back box, but some of my back boxes are plastic and if that was to catch fire, god knows what could of happened. Has anyone else experienced this?

I can’t measure the voltage as I am not happy to plug the devices back into the mains. Please see attached picture