Cloud storage rarely stops syncing at random. The causes are a small, predictable set: a full quota, a paused or signed-out client, selective sync hiding folders, a filename the service rejects, a file locked open by another app, or a VPN or firewall blocking the connection. Match the symptom to the cause, then apply the one fix that addresses it.
The instinct when files stop moving is to reinstall the client or drag everything in again. Both usually make it worse. Diagnose first.
Why do files sit "uploading" and never finish?
A permanently spinning upload indicator points at one of four things, in order of likelihood.
The account is at its storage quota. Most clients keep trying and show a generic "syncing" state rather than a blunt "you're full" error, making this the most-missed cause. Check used-versus-total storage in the web interface — and remember deleted files often sit in a trash area consuming space until it's emptied.
One locked file is blocking the queue. Clients process a queue, and a single unreadable file holds up everything behind it. Files open in another application — an active database, a spreadsheet with an editor lock, an in-progress render — are often unreadable to the client. Close the app that owns the file.
The file exceeds a per-file size cap. Services impose maximum single-file sizes, and the limit may differ between desktop client and web uploader. If one huge file is stuck while small ones fly through, that's the likely culprit.
Something is interfering with the connection. Covered below — a VPN, proxy, or firewall can stall a transfer rather than fail cleanly.
Why did a file disappear from one device but not another?
Usually the file was never deleted — it just isn't being kept locally on that device.
Selective sync (also called smart sync, files-on-demand, or online-only files) keeps folders in the cloud without occupying local disk. A folder excluded on your laptop is still in the account; it just isn't downloaded. Re-enable it in the client's settings. This explains most "the file vanished" reports.
Genuine deletion propagates everywhere, quickly — that's sync working as designed. If the file is gone from the web interface too, restore it from the trash. Retention windows vary by provider and plan, so check sooner rather than later.
Someone revoked a share. A file in a folder another person shared with you disappears when they unshare it. Nothing is broken; access simply ended.
This is the distinction covered in our cloud storage buyer's guide: sync keeps your current files identical everywhere, which is not the same job as keeping recoverable past copies.
What are conflicted copies, and why do they keep appearing?
A conflicted copy — a duplicate suffixed "(conflicted copy)" or with a device name appended — appears when the same file was edited in two places before either edit reached the server. The client can't know which version you want, so it preserves both. That's good behavior; the alternative, silent overwrite, is how work disappears without a trace. If conflicts appear constantly, the cause is one of these:
- A device was offline while you edited, then reconnected to find the file already changed elsewhere.
- An always-open application holds the file, writing continuously and never releasing a clean state.
- Two people are collaborating in a format with no real-time merge. Desktop office documents in a shared folder generate conflicts constantly; web-native collaborative editing solves exactly this.
The fix is procedural: let a file finish syncing before opening it on a second device, and use the collaborative editor for anything two people touch at once. Never delete a conflicted copy before comparing it — it may hold the newer work.
Why does the client refuse specific files?
Some files never sync no matter how long you wait, because the service or the filesystem rejects them outright.
Restricted characters and names. Windows disallows \ / : * ? " < > | in filenames, plus reserved names like CON, PRN, AUX, and NUL. A file created on macOS or Linux with a colon in its name lives happily there, then fails to land on a Windows device. Rename to plain alphanumerics, hyphens, and underscores; leading or trailing spaces and dots cause similar trouble.
Path length. Deeply nested folders can exceed the maximum path length the OS or client supports, especially on Windows. Shorten folder names or move the tree closer to the drive root.
Local disk is full. A device with no free space cannot download incoming files, so sync stops in one direction while uploads look fine.
Can a VPN or firewall break cloud sync?
Yes, and it's under-diagnosed. Sync clients hold persistent outbound connections, and anything that reroutes or inspects that traffic can degrade them. A VPN routes traffic through a distant server, slowing large transfers enough that they look stalled. Firewalls and TLS-inspecting proxies can interrupt connections entirely, and antivirus real-time scanning occasionally locks a file mid-sync.
The diagnostic is simple: disconnect the VPN, or move to a different network such as a phone hotspot. If sync resumes, you've found the layer at fault — see our VPN buyer's guide on what a VPN does to your routing. Note the kill-switch interaction: if your VPN blocks all traffic when the tunnel drops, sync halts silently until it's restored. That's the feature working, not a bug.
Symptom, cause, and fix at a glance
| Symptom | Likely cause | Fix |
|---|---|---|
| Upload spins forever, never completes | Storage quota reached | Check used vs. total storage; empty the trash area or upgrade the plan |
| One large file stuck, small files fine | Exceeds the per-file size limit | Check the service's maximum single-file size; split or compress the file |
| Sync stalls on one specific file | File locked open by another app | Close the app that owns it, then let the queue resume |
| Missing on one device, present on the web | Selective / online-only sync excludes it | Re-enable the folder in selective sync settings |
| File gone from every device | Genuinely deleted; the deletion synced | Restore from the trash area within the retention window |
| Duplicates marked "conflicted copy" | Edited in two places before syncing | Compare and merge manually; edit one device at a time or use the web editor |
| Specific files never sync at all | Restricted characters, reserved names, long path | Rename using plain characters; shorten deep folder paths |
| Downloads stop, uploads seem fine | Local disk is full | Free space, or move folders to online-only |
| Client shows "not connected" | Expired session or revoked device | Sign in again and re-authorize the device |
| Everything stalls on one network only | VPN, firewall, proxy, or antivirus | Disconnect the VPN or switch networks; allow the client through the firewall |
| Stuck "indexing" after reinstall | Full re-scan of a large library | Leave it on power and a stable connection; large libraries take hours |
Work top to bottom; usually one of the first four rows is the answer.
When is the real problem the service, not the setup?
Some sync problems are the product. If you routinely lose work to silent overwrites, or the client needs restarting to notice changes, you're not misconfiguring anything — you're using a weak sync engine. Judge that with criteria set before you shop: sync reliability, conflict handling, version history depth, and client quality on every platform. Our criteria-first comparison framework covers how to weight those against price and test them in a trial.
FAQ
How long should a normal sync take?
There's no universal number — it depends on file sizes, upload speed, and whether the client uses block-level sync (sending only the changed portion of a file) or re-sends the whole file on every save. What matters is progress, not duration: if the queue count is falling and transferred bytes are rising, it's working. A counter frozen for fifteen minutes on a healthy connection is a genuine stall.
Will restarting the sync client fix things?
Often, and it's a safe first step. Quit fully — from the system tray or menu bar, not just closing the window — then reopen. That clears a wedged queue and forces a fresh connection. What you shouldn't do reflexively is uninstall and reinstall: that can trigger a re-index that looks identical to a hang for hours.
Can I lose files permanently through a sync error?
Yes, if you rely on sync alone. A deletion or overwrite propagates everywhere, and your only recovery is version history and trash retention — both limited, with limits that vary by provider and plan. Check the retention window on your tier, and for anything irreplaceable keep an independent backup sync cannot reach. Losing access to the account itself is a separate risk; see our guide on evaluating account recovery options.
Does pausing sync stop my files from uploading?
Yes — anything you edit while paused exists only on that device until you resume. Clients pause automatically on metered connections or low battery, and users often pause during a big transfer and forget. If files seem stale, check the pause state first — it explains a surprising share of reports.
Sync reliability, version history depth, and conflict handling are exactly the criteria we score, service by service. Compare cloud storage services on sync reliability and version history at top-fully.com.
