Here is a quick troubleshooting for Google Drive.

1- Click on your profile picture>Set up this team >App extensions
2- Click on the red icon  to disconnect Clustdoc from Google Drive

3- Flush your cookies
4- Reconnect Google Drive to Clustdoc
5- Launch the synchronization again

If you don't mind switching to another Cloud, we also recommend trying out DropBox. 

 What triggers the automated files backup?

As soon as an application is updated (by one of your team members, by yourself or by a client: new document uploaded, new message, etc), the CLUST folder created in your Drive will be updated every hour. 

You may want to manually sync' existing applications if you want to send them right away to your Cloud.

 What triggers the manual synchronization?

You need to go in your application (In the File export tab) and click Synchronize to start the process.