Missing files

I finished about 29 illustrations for a book in Fresco on my iPad. After they were done I put them into a folder in the "Your Files" tab. I went back later the same day to access one of the files and the folder said it was empty. I quit Fresco on the iPad. Then went back in. All the files showed in the folder and I was able to access the file I needed. The next day I went back in to double check that the files were there and they were all gone again. I went to the Cloud app and they weren't there either. I can see about half of them in the recent files on the home tab. If I continue to Use Fresco, I fear I will loose access to all of the files. I cannot see any of them in the "Your files" tab any more. How do I get them back?