The analysis tool is usually needed for this issue:
Download and then install the msi.
On the root of the C drive there will now be a folder caller ReplibitAtalysisTool Run the tools executable as admin.
It is often due to a network or resource bottleneck somewhere, and the analysis tool will help to identify this. Follow the above KB and run the Replibit Analysis Tool. Open a ticket with Replibit Support if needed.