I saw something that looked like lots and lots of tiny scratches on my glasses. They are almost invisible in bad lighting, but clear when looking at them in sunshine. The seller didn't even care to look at them, just told me surface treatment probably had crackled. She also said that heat is often the culprit, like using them in the sauna.
But I hadn't been using them in the sauna and had also avoided the steam coming out from the oven when opening the oven door. Also been really careful when cleaning them.
I tried to find images of crackled glasses on the web to compare with, but found nothing. So, to provide the web with content, here are images of my old, probably crakled glasses and of my new ones for comparison.