Hi Springer Christian
If the DDB backup does not get past 0%, that means it has not gone into the FileScan phase on the MediaAgent to determine the file structure of the DDB.
If restarting CIF's help, there could a write request stuck between the MediaAgent and the Disk Library, causing all other operations within Commvault to fail.
Do we see any issue from the Disk Library? As you are using CIFS you will be leveraging SMB from the Windows layer to get access to the Disk Library, can you please check with your network or storage team what is happening during this time frame and whether there are any stuck IO's or hung issue (from storage level)?