I experienced sudden crashes/reboots of TrueNAS 12.0-RELEASE during replication of a dataset to a USB-attached local pool consisting of a single disk vdev.
I ruled out hardware issues by replicating the issue on a virtualized TrueNAS instance with virtualized disks on separate hardware. No hardware implicated in the original crash was used in the virtualized instance.
I have isolated the files that cause the crash/reboot to two (broken) symlinks in a particular dataset and can provide those files for inspection. Other broken symlinks do not cause this issue.
Please see https://www.truenas.com/community/threads/zfs-replication-to-usb-drive-caused-nas-reboot.89152/ for more details.