ZFS operations hanging, but no visible errors?

Hey there.  I have a server running FreeBSD 13.0-RELEASE, with a large ZFS zpool.  I have a UFS mirror on hardware raid, then a bunch of JBOD disks in a pool.  I recently added a new vdev to this pool, which may or may not be related.

Today, I started an rsync of a large (100GB) file from the pool to another host.  After a while (7%), it seemed no progres was being made.  I tried to kill the rsync, which didn’t exit, or suspend.  Now anything that touches the pool seems to hang.  But, the system is otherwise functional, console shows no issues, the controller (via out-of-band management interface) shows all disks as having no errors or issues.

Any idea what I should be looking for, and if there’s any way to recover it without reboot?  Another operation I had running was in the middle of writing data I’d rather not lose progress on, which is why I haven’t rebooted yet.

               - Chris