Enamel chipping off on corners

[corsin.b]

Hello everyone,

I have been having trouble with enamel chipping off on the corner of my pieces:

It's on 2mm and 3mm steel with a groundcoat and then 2-3 layers of white enamel and then a decal transfer.
steel tiles are sandblasted before application and it has happened both when I did or did not counterenamel. Some of them have also not chipped off until days or even weeks after the last firing.

anyone have any idea what could be causing the issues?