Fix Cloud Sync Stuck at 99% or Hanging — Troubleshooting Stalled Transfers in RcloneView
The progress bar says 99%. It's been saying 99% for 45 minutes. Is it working? Is it stuck? Should you cancel? Here's how to diagnose and fix stalled cloud transfers.
Stalled cloud transfers are one of the most frustrating issues in cloud sync. The job appears to be running, the progress indicator barely moves, and you're unsure whether to wait or restart. The good news: stalled transfers almost always have a specific, fixable cause.
Manage & Sync All Clouds in One Place
RcloneView is a cross-platform GUI for rclone. Compare folders, transfer or sync files, and automate multi-cloud workflows with a clean, visual interface.
- One-click jobs: Copy · Sync · Compare
- Schedulers & history for reliable automation
- Works with Google Drive, OneDrive, Dropbox, S3, WebDAV, SFTP and more
Free core features. Plus automations available.
Common Causes
1) Large file nearly complete
The most common "false alarm." A 50 GB file at 98% complete still has 1 GB left. At 10 MB/s, that's another 100 seconds — but the progress bar barely moves because it's measuring file count, not bytes.
Fix: Monitor the transfer speed indicator. If bytes are still flowing, the transfer is working — just slow on the last large file.
2) API rate limit throttling
Google Drive, OneDrive, and other providers throttle transfers when you hit API limits. The transfer slows to a crawl but doesn't fail.
Fix: Reduce concurrent transfers. Add --tpslimit via the built-in terminal.
3) Network timeout on large file
Some providers disconnect long-running uploads silently. The transfer appears active but no data is moving.
Fix: Configure timeouts in your remote settings. Use --timeout to detect stalls earlier.
4) File locked by another process
The source file is open in another application. The transfer waits for access.
Fix: Close applications that might be using the file, or exclude actively used files with filters.
5) Provider-side processing
Some providers process uploaded files (virus scanning, indexing) before confirming completion. This creates a gap between upload completion and confirmation.
Fix: Wait. This usually resolves in 1-5 minutes.
6) Memory exhaustion
Very large transfer lists (millions of files) can exhaust available memory, causing the process to slow dramatically.
Fix: Break the transfer into smaller batches by folder.
Diagnostic Steps
Check job history
Use the terminal for verbose output
Run the same operation from RcloneView's terminal with -vv flag for detailed diagnostic output.
Cancel and re-run
If the transfer is truly stuck, cancel and re-run the job. RcloneView skips already-transferred files and resumes from where it stalled.
Prevention
- Set reasonable timeouts in remote configuration
- Use modest concurrency (4-8 transfers) to avoid rate limits
- Break large jobs into smaller batches
- Schedule retries — if a nightly job stalls, a second scheduled run catches up
Getting Started
- Download RcloneView from rcloneview.com.
- Check transfer speed — if bytes flow, it's working.
- Reduce concurrency if rate-limited.
- Cancel and re-run if truly stuck.
99% complete and stuck is almost always the last big file finishing slowly.
Related Guides:
Supported Cloud Providers
