Yeah, I had the syslog server on historically for troubleshooting. I've turned it off and will move /system/ back to cache and report back if I have any other issues with the locking of zfs datasets.
Moving the system folder off of the zfs dataset seems to have resolved my issue. I'm going to guess it's because of the always in-use syslog files. That's pure speculation though, if anyone has more information.
Thanks!
I was trying to take my array offline this morning, and was met with the same issue.
I ended up doing sudo shutdown -r now via command which seemed to kick the server, albeit uncleanly.
I'm going to move the system share off of cache to see if that resolves my issue.