file upload stuck at 100%" common causes

TL;DR

100 percent usually means the bytes arrived but the server never finished processing them, so the file is not lost, it is in limbo. Do not let the user re-upload blindly, because that often creates duplicates. Check whether the file landed on the server first, then look at processing, file size, and anything scanning the file mid-upload.

The query

"file upload stuck at 100%" common causes

Use this when

• The progress bar reaches 100 percent and freezes
• The upload "completes" but the file never shows up
• Users report having to upload twice to make it stick
• Large files stall at the end while small ones work
• You are writing the upload-troubleshooting macro

Not for

• Uploads that fail at 0 or 10 percent
• Files rejected for type or size limits
• The whole network dropping mid-upload
• Download problems, which are a separate path

Steps

1. Check whether the file actually arrived

Before anything else, look in the destination on the server side. In most of these cases the file is sitting there waiting for processing. If it is there, tell the user not to re-upload.

Expected output: the file is confirmed present or confirmed missing.

2. Wait out the processing step

After the bytes land, the server usually scans, converts, or generates previews, and the progress bar does not reflect that. Large PDFs, videos, and spreadsheets can take minutes. Tell the user to leave the tab open and give it five minutes before touching anything.

Expected output: the file appears on its own, or the wait is ruled out.

3. Check the file size and type

Oversized files and exotic formats stall processing most often. Compare against your documented limits, and ask the user for the exact size. A 2 GB video on a 500 MB limit will sit at 100 percent forever rather than erroring cleanly.

Expected output: size and type confirmed within limits, or the real rejection found.

4. Rule out antivirus and browser extensions

Desktop antivirus that scans uploads in real time can hold the final bytes hostage, and ad blockers sometimes interfere with the completion request. Have the user retry with extensions disabled, or from a different browser.

Expected output: a clean retry that finishes, or extensions ruled out.

5. Retry with a smaller test file

If the big file still will not finish, have them upload a tiny file of the same type. If the small one works, the problem is size or content specific, and you have a clean repro to hand engineering.

Expected output: a working small upload, or proof the path itself is broken.

Ready-to-use message

Good news: 100% usually means your file arrived and our side
is still processing it, not that it's lost.

Please leave that tab open for 5 more minutes without
re-uploading. If the file still hasn't appeared, tell me:

1. The file name and size
2. Which browser you're using

And don't upload it a second time yet, that tends to create
duplicates we then have to clean up.

Variant phrasings

upload freezes at 100 percent and never finishes

Steps 1 and 2. The file is probably there. Patience first, debugging second.

uploaded file not showing up after complete

Steps 1 and 5. Confirm server-side, then test with a small file.

large file upload stuck support

Steps 3 and 5. Size limits and processing time scale together, so test small.

Why it happens

Progress bars measure bytes sent, not work done. The last step, virus scanning, transcoding, thumbnailing, indexing, is invisible to the bar, so the user watches 100 percent sit there and reasonably concludes it broke. The fix is mostly expectation-setting plus checking the server side before anyone re-uploads.

Edge cases

• The file appears twice after the user re-uploaded: delete the duplicate and explain the wait rule for next time.
• Uploads stall at 100 percent only on the office network: corporate proxies sometimes buffer the final request. Test from a phone hotspot to confirm.
• The file appears but previews never generate: the bytes are fine and the processing worker is the problem. Escalate with the file attached.
• User closed the tab at 100 percent: check the server before assuming loss. Many systems finish processing even after the tab closes.
• Every file type works except one: that format's processing pipeline is broken, not the upload path. Narrow the repro to the format.

Provenance

Resolved from the public thread: https://vectle.com/posts/pstYhJJVQSdavT5v4jGlQaGw