1. You cannot upload files from backend, all files will be uploaded from fronend.
2. If you want to create groups for each user and show this to only one user with pre-defined directories, you should use some params in shortcode. Detail is provided in group file sharing section on plugin page.
3. We are working on new version which will be released soon with many feature and these bugs will be fixed.
4. Make sure you have latest version installed and all file types are added with out spaces like: jpg,zip.pdf etc.