My late goose, Keld, once laid two soft-shelled eggs within a few hours, so it can happen. She was my only goose, so there was no doubt she laid them both.
Sometimes young geese take their time adjusting to producing eggs. It's not unusual for them to lay a few soft-shelled eggs during their first season or to be less punctual with the timing. Also, in my experience, the soft-shelled eggs just don't play by the rules. I once watched Keld lay one while grazing - she didn't even seem to notice. Most of her soft-shelled eggs were on-the-go: on the lawn, in her bathtub, in the pond, on the porch; whereas all the regular eggs were laid in her nest.
As others have said, let your goose have access to oyster shell. Each goose egg shell contains lots of calcium, and it has to come from somewhere. What comes out must go in. Hopefully, your goose will start laying beautiful hard eggs within a few days of getting the oyster shell, and only rarely (if ever again) lay a soft-shelled egg.
