Why large file uploads fail, and how to stop losing progress
Twenty gigabytes of RAW files, forty minutes into the upload, and the progress bar resets to zero. Big uploads fail more often than small ones, and for reasons that have nothing to do with how fast your internet is. Here's what actually goes wrong partway through a large upload, and how to send big files without losing your progress every time it happens.
Why big uploads fail more than small ones
A five minute upload only needs five minutes of uninterrupted connection. A ninety minute upload needs ninety minutes straight, on a WiFi network that can drop for a few seconds, a laptop that can go to sleep, and a browser tab the operating system can decide to close to save memory. None of those risks go away as a file gets bigger. They just get more time to happen.
That's the real reason a 40 MB export sails through and a 40 GB video project stalls twice before it finishes. It's not your connection getting worse. It's the odds catching up with you.
The most common failure points
- An unstable connection. WiFi drops for a few seconds, a chunk times out, and the progress bar stalls or jumps backward.
- The device sleeps or the tab closes. A laptop lid closes, or the browser reclaims memory from a tab you switched away from, and the upload has nothing left to run on.
- The file is still syncing from cloud storage. iCloud, Dropbox, and Google Drive can show a file as available when it's actually a placeholder that hasn't downloaded to your device yet.
- You're over your plan's size limit. The upload gets rejected before it starts, which can look like a failure even though nothing actually broke.
- A browser extension gets in the way. Ad blockers and privacy extensions sometimes intercept the network requests an upload depends on.
What each symptom actually means
Not every stall is a failure. Here's how to read what you're seeing before you assume the upload is broken and start over.
| What you see | What's actually happening | What to do |
|---|---|---|
| Progress jumps around or pauses | A piece of the upload failed and is retrying on its own | Give it a minute on a stable connection before assuming it's stuck |
| Stuck at 99 or 100 percent | The server is assembling the finished file from its pieces | Leave the tab open until you see the confirmation screen |
| Upload restarts from 0 percent | The tab closed or the browser lost the file reference | Reselect the file, then keep the tab open and the device awake |
| “File cannot be read” error | The file is mid-sync from cloud storage, or was moved after selection | Wait for the sync to finish, then remove and re-add the file |
| Rejected before it starts | The file, or your whole selection, is over your plan's limit | Check your plan's size limit and split the upload or upgrade |
Fix the causes you control
Most of this comes down to two things: a connection that stays up, and a tab that stays open and awake for the whole upload.
- Use a wired connection instead of WiFi for anything over a few gigabytes if you can.
- Keep the tab open and your device awake until you see the confirmation screen, not just until the bar looks full.
- Let cloud synced files finish downloading to your device before you select them for upload.
- Turn off ad blockers or privacy extensions if an upload keeps failing at the same point every time.
- Upload from a computer instead of a phone for anything large. Mobile browsers close background tabs faster.
Why some tools recover and others make you start over
The real difference between a transfer tool that survives a bad connection and one that doesn't is whether it uploads in chunks. ZappFiles splits every upload into pieces and retries a failed piece on its own, up to three attempts, without touching the parts that already made it through. If your WiFi drops mid-upload, it pauses and picks back up from where it left off the moment you're back online, not from zero, as long as the tab stays open. The full behavior is covered in the upload troubleshooting guide.
Enough room that you're not fighting the limit too
You can send up to 3 GB without an account, 5 GB with a free account, 50 GB on Pro, and 250 GB on Max, so a large RAW gallery or a 4K export doesn't put you anywhere near a rejected upload in the first place. Full limits per plan are on the file size limits page. If your files are small enough for email but keep bouncing anyway, that's a different problem, covered in our guide to email attachment size limits.
A quick checklist before you try again
- Check your connection first. A wired connection beats WiFi for anything large.
- Confirm the file has fully downloaded from any cloud storage folder before you select it.
- Keep the tab open and the device awake for the entire upload, not just until the bar looks close to full.
- Check your plan's size limit if the upload fails immediately instead of partway through.
- If it still fails at the same point every time, try a different browser with extensions disabled.
Upload large files without starting over
Chunked uploads that retry on their own and resume where they left off, up to 250 GB per transfer.