In case your Gateway Server and Access server go out of sync, your data sources will not be accessible by mobile clients. This is a very rare occurance, to fix it, do the following:

1. Open the Acronis Cyber Files web interface and log in as an administrator.
2. Navigate to Mobile Access -> Data Sources.
3. Open the desired Data Source and press the Save button. You need to do this for all Data Sources linked to the un-synced Gateway Server.