I just enabled Time Machine backups on SMB today, and sometime between enabling it and starting to back up my computers, I got a notification that SMB had core'd.
I only have 1 core, so it's not a pervasive issue, and I noticed that there are a couple of other open bugs that have similar symptoms, but since I have no way of knowing if it's the same bug I'm filing a new issue:
I'm attaching my core file and system debug report.
This is a clean install of 12.0-U2.1.
root@truenas[~]# ls -l /var/db/system/cores
-rw------- 1 root wheel 197271552 Mar 27 14:33 smbd.core