The issue occurs when the block size that the Backup Copy job expects does not match the actual block size of the restore points created by the source Backup job(s).
As documented in the User Guide:
A backup copy job does not copy a restore point if its data block size differs from the data block size of restore points that the job has already copied to the target backup repository. To copy restore points with the changed block size, you need to create active full backups. For details, see Change Storage Optimization Settings for Backup Copy Job.
For example, if you have changed the block size for restore points in the source backup job (the Storage optimization option in the Storage Settings), Veeam Backup & Replication will not copy newly created restore points and will display the Restore point is located in backup file with different block size message.