Replication task fails with massive error: 'pool or dataset is busy cannot unmount'

[nigon]

As part of another, unrelated issue (https://www.truenas.com/community/t...that-have-different-numbers-of-drives.114316/) I've created a temporary second TrueNAS scale server for the point of creating a full filesystem replication that I can restore later. However, the full replication task fails consistently after about 8-10 hours. It produces an absolutely massive error that's too large to practically stick in a single forum comment or screenshot. However, the error is broken down into three message types, each repeated dozens of times for different snapshots or filesystems:

Code:

skipping snapshot plex@auto-2023-11-24_00-00 because it was created after the destination snapshot (auto-2023-11-23_00-00) 
skipping snapshot plex@auto-2023-11-25_00-00 because it was created after the destination snapshot (auto-2023-11-23_00-00) 
skipping snapshot plex@auto-2023-11-26_00-00 because it was created after the destination snapshot (auto-2023-11-23_00-00) 
skipping snapshot plex@auto-2023-11-27_00-00 because it was created after the destination snapshot (auto-2023-11-23_00-00)

Code:

 send from @auto-2023-11-22_10-58 to plex@auto-2023-11-23_00-00 estimated size is 624B 
full send of plex/plex-config@auto-2023-11-23_00-00 estimated size is 1.99G 
full send of plex/plex-media@auto-2023-11-23_00-00 estimated size is 4.55T 
full send of plex/.system@auto-2023-11-23_00-00 estimated size is 1.35G

Code:

cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy
 cannot unmount '/var/db/system/rrd-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/samba4': pool or dataset is busy 
cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/rrd-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/samba4': pool or dataset is busy 
cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/syslog-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/rrd-f1f5036a6e4448d09a9ddb3c45165866': pool or dataset is busy 
cannot unmount '/var/db/system/samba4': pool or dataset is busy Broken pipe.

The first two ("skipping snapshot...") and ("full send size is...") seem somewhat informational, while the last one seems like an actual error. Can't seem to find a solution online, so I've either hit something very weird or I've done something super dumb.


Source TrueNAS server:

OS Version:TrueNAS-SCALE-22.12.3.3
Product:Super Server
Model:AMD EPYC 7302 16-Core Processor
Memory:63 GiB

Destination TrueNAS server:

OS Version:TrueNAS-SCALE-22.12.3.3
Product:PowerEdge R720
Model:Intel(R) Xeon(R) CPU E5-2630 0 @ 2.30GHz
Memory:59 GiB

The replication task:

The source dataset: