Having experienced this with our plug socket - I agree. 100% they can be a thermal bridge on an external cold wall. In addition to plug sockets on dry walls, it’s making me think about metal handles on upvc doors and windows.
@lloydham posted about a very wet internal door handle on his A+ rated door. With the very valid question
’should this happen?’
My window fitter spoke of letter boxes and door handles in relation to them failing the thermal performance of all the other specialist materials used on windows and doors.