Greyfox7. Probably worked for me because the SP3 had been in the bag for a couple of hours so it was cold. And the weather was cool too.
Probably wouldn't work during summer here.
So the glass has to be cold I think for it to work.
Wasn't something I wanted to take any action on at this stage as apart from the occasional wifi/Bluetooth problem the SP3 is fault free.
Just curious if it's a one off or the same on all SP3's.
I'm thinking it looks like it's the result of something that's used in production to lift the glass in production. Almost like it's an oily deposit. But I'm a bit reluctant to try any cleaners etc.