11.2-RELEASE-p11 hang on shutdown

[Craig Leres]

I have a server with a Supermicro X11DPU motherboard. If I "shutdown -r 
now" or "shutdown -p now" the system hangs as if I did "shutdown -h now":

     Waiting (max 60 seconds) for system process 'vnlru' to stop... done
     Waiting (max 60 seconds) for system process 'bufdaemon' to stop... done
     Waiting (max 60 seconds) for system process 'syncer' to stop... done
     Syncing disks, vnodes remaining... 0 0 0 0 0 0 0 0 0 done
     All buffers synced.
     Uptime: 1d19h56m19s

At this point only using the reset or power buttons (or ipmi equivalent) 
can get the system back.

The only filesystems are zfs using six Intel 905P nvme 2.5" drives:

     zinc 6 # zpool status
       pool: tank
      state: ONLINE
       scan: scrub repaired 0 in 0h1m with 0 errors on Wed Jul 17 
20:01:36 2019
     config:

             NAME        STATE     READ WRITE CKSUM
             tank        ONLINE       0     0     0
               mirror-0  ONLINE       0     0     0
                 nvd0p3  ONLINE       0     0     0
                 nvd1p3  ONLINE       0     0     0
               mirror-1  ONLINE       0     0     0
                 nvd2p3  ONLINE       0     0     0
                 nvd3p3  ONLINE       0     0     0
               mirror-2  ONLINE       0     0     0
                 nvd4p3  ONLINE       0     0     0
                 nvd5p3  ONLINE       0     0     0

     errors: No known data errors

What can I do to get some hints where things are hanging?

		Craig