Unstable internet connection. Solution: Switch to a wired Ethernet connection. For very large uploads, use the Katsem Bulk Uploader application (if available) as it supports resumable uploads.
For the end-user, visual feedback is essential. Katsem provides real-time progress bars and "success" notifications, reducing the "did it actually work?" anxiety often associated with web forms. How to Implement Katsem File Upload (For Developers) katsem file upload
After selecting files, Katsem may present a form asking for: Unstable internet connection