When using Synology's Hyper Backup app on an encrypted volume to rsync a backup from Synology to FreeNAS it sends long file paths. These long file paths aren't supported in the rsync 3.1.3 running on FreeNAS.
This issue has been reported twice before without resolution. There is a hint that it got raised to Synology, but we don't know that result.
Attached is the section from stor001:/var/log/messages of when the Synology, named aion, tried sending files.
syncd: ERROR: buffer overflow in recv_file_entry [receiver]
Rsync on FreeNAS: 3.1.3
Synology DSM: 6.2.2-24922-3
Hyper Backup: 2.2.1-1110