If you have sync issues in the Documents app, there are some steps you can take in order to troubleshoot the problem. 

Step 1

First, please make sure you have a stable network connection. Try disabling the Wi-Fi, enabling it again, then open Documents > Synced folder > pull down to refresh and trigger the sync process.

Step 2

If the sync issue persists, try disconnecting the cloud storage account from the app and connecting it anew.

To disconnect the storage from the app:

1. Find in your cloud storage folder in the My Filessection in Documents. If you use iCloud, it's either the Documents – iCloud or the Files folder.
2. Tap three dots on the folder.
3. Tap Delete (if some changes were not synced to the server, save the file's copy locally).

To set up the connection anew:

1. Tap the Pluss button  > Add Connection.
2. Choose the needed storage.
3. Sign in again.

Then, retry to sync your folders again to see if it helped.

Step 3

If you're using Dropbox:

Dropbox sync errors can be caused by the specific copyrighted file if its sharing is restricted by Dropbox's copyright policy.

If you sync a file and its sharing is restricted by Dropbox copyright policy, you will see an exclamation mark on the folder and a Restricted content error on the file thumbnail. Remove the file from the folder to get rid of the error message.

If you're using iCloud:

Go to iOS Settings on your device > tap your name to enter the Apple ID settings > iCloud > toggle it off/on for Documents. This will trigger the sync process if the upload or sync to iCloud doesn't seem to be working properly. 

If you're having trouble adding a OneDrive for Business account:

If your account uses conditional access, the admin of your organization should configure the rights for your account - you can refer to this article for the instructions. 

To help us with further investigation, please also try these steps: 

1. Please try connecting to your account in the OneDrive app.
2. Try connecting to your account in Documents Settings  >  Clouds & Connections > SharePoint tab.

If you're using other services:

Some cloud services impose special character restrictions for the names of files and folders. Using such special characters might lead to sync errors. If restricted characters are used in the titles of files and folders, you will see an exclamation mark on the folder and an unknown error on the file thumbnail. Please check your cloud service support section for more information on special character limitations.

If you're connecting by using any supported protocols (WebDAV, SMB, FTP, SFTP), please keep in mind that the credentials are case-sensitive. 

Step 4: Contact Us

1. Open Documents Settings  > Support.
2. Tap Send feedback. Screenshots illustrating the errors you’re getting (if there are any) will help us see the situation more clearly.