Did you ever find a solution to this? We have a machine in a similar situation
although seems to suffer on 5.4 as well. It had been fine for months but
suddenly after a restart it would hang initialising jails with processes
blocked in state "ufs".
We've tried to upgrade to 6.1-RELEASE-p10 but in
Recently I tryed to update 5.4 to 6.1 from sources.
After successfull install I found that all processes (pkg_delete, pkg_add, cp,
tar, etc..) I run hangs mostly in getblk state.
I reinstalled 5.4. It works fine.
So I installed only the kernel from 6.1-R and booted it in single user mode.
The pro