Do you also have the Selfie Shape Correction turned on?
I found a temporary workaround until Samsung gets this fixed. I have an S9+ and there is a picture mode called "Live Focus". If you put it in that mode the picture turns out as previewed.
I think i may have figured out what was wrong or they fixed it in a recent update. If you see the option with the person and then the group when you have the front face camera open. If it's set to the single person it zooms it. But the group setting doesn't.