I am havin the same problem with MacBook Pro 2016>The magnetic is working on screen.I test it passing a clip paper around bezel ….my problem it would be on lower case. I will try to test with a magnet like you did.
same problem here with a MBP late 2016 , I bought it in Miami and I live in Brazil. It's frustrating dedicate extremely care for a computer and watch it breaks by itself, in normal use. Apple, please, recall everybody, at least from 2016 to solve this common issue.