Explanation
https://helpcenter.veeam.com/archive/backup/110/hyperv/guest_interaction_proxy.html According to the Veeam Software Help Center1, Veeam Backup & Replication deploys runtime components on a VM guest OS to perform file indexing. These components can be either non-persistent or persistent depending on whether you have enabled application-aware processing for the VM.
If you have enabled application-aware processing for the VM, Veeam Backup & Replication uses a persistent agent component that is installed on the VM guest OS during backup job session and remains on the VM after that. In this case, if the guest interaction proxy is offline, Veeam Backup & Replication will use another available guest interaction proxy or fail over to the backup server.
If you have not enabled application-aware processing for the VM, Veeam Backup & Replication uses a non-persistent runtime component that is deployed on the fly and removed after indexing is complete. In this case, if the guest interaction proxy is offline, Veeam Backup & Replication will use another available guest interaction proxy or fail over to the backup server.