You have been successfully backing up and recovery points are created successfully, however, there is a warning when the retention rules are applied:
Cannot free up space taken by the deleted backups. The operation will be retried during next backup deletion.
Such issue also occurred on Linux agents, 32-bit versions.
This is expected behavior for the backup and recovery process.
If you browse the backup 10-20 minutes prior the backup job, the slice gets locked to allow you browsing it. However, the full access to the slice is required for the retention job. As the Agent cannot acquire the full access, the warning appears.
This issue has also been observed more frequently with Agents for Linux (32-bit).
The issue with Linux 32-bit Agents is fixed in Acronis Agents builds starting from 4500.
As the error message states, the deletion will be retried next time. If the archive is not locked by then, the archive will be cleaned up before the next backup.
The issue does not affect the health of the backup.