The stamp creator presumes you have a piece of engravable art - and it reverses it and ads the cut lines, so you may have been making yours too ready! Try just your art, no edges and see if it works. If it doesn’t you probably want to post in P&S with screenshots showing exactly what’s happening.
Also, MoaG is for complete art so I’m moving your post to Everything Else.
I’ve only played with the stamp creator a couple times–but there is an option to keep the original artwork or not. So check you have it to keep the original.
But even with that, I have the same “it’s gone!”–but no, it’s there–if you move the new stamp outline, you’ll see the original–not sure why it appears to be invisible when under the stamp overlay! Maybe we’re just lucky?