Assuming that you put the backup repositories in the backup network only, what possible issue...

A possible issue that could arise if you put the backup repositories in the backup network only is that laptop agents cannot communicate with the repository. This is because laptop agents are not part of the backup network, which is non-routable according to the existing technical environment.Therefore, laptop agents cannot access or write data to the backup repositories in the backup network unless there is a proxy or gateway server that can bridge the communication between them.

References: [Veeam Agents Management Guide], [Veeam Backup Infrastructure Sizing Calculator]