I have this quarter that multiple self checkouts will not take. It looks normal to me. I don't have a scale that is sensitive enough to see if it is off weight. Compared to others, the size seam correct. Odd.
I rarely have change in my pockets. I use a rewards card for 99% of my purchases. Ya gotta be a fool not to, they build that into the price of goods you know.
Not magnetic. When I hold it next to another quarter, there is nothing obviously different. Do some of these machines use a photo to compare? Maybe that one design is not in the system. They don't work like that way as far as I know.