Issue with Object Scanning Target & Scanned Object

I'm trying to scan a bunch of shoes. A few of the others were successful and tested in the Object Scanner App worked fine. Some of the shoes initially scanned ok, but when I remove the Object Scanning Target paper, the grid disappears and the scan becomes useless. Can anyone tell me what I'm doing wrong or why when I remove the piece of paper, it doesn't work. I tried both to remove paper first or remove the shoe first and still doesn't work. But for the other shoes, I did it the same way and worked. Thanks for any input.