panic: nfsv4root ref cnt cpuid = 1

After upgrading to 14.1-RELEASE-p4, we have a machine that
spontaneously reboots every day or so with the message above.

The stack trace from dmesg.boot shows:

panic: nfsv4root ref cnt
cpuid = 1
time = 1727011803
KDB: stack backtrace:
#0 0xffffffff80b7fefd at kdb_backtrace+0x5d
#1 0xffffffff80b32bd1 at vpanic+0x131
#2 0xffffffff80b32a93 at panic+0x43
#3 0xffffffff809da294 at nfsv4_relref+0x34
#4 0xffffffff809e5723 at nfscl_openrelease+0x63
#5 0xffffffff809f9eef at nfsrpc_lookup+0x87f
#6 0xffffffff80a0e2fd at nfs_lookup+0x43d
#7 0xffffffff80c0341a at vop_sigdefer+0x2a
#8 0xffffffff8302c3a7 at null_lookup+0xc7
#9 0xffffffff80c08745 at vfs_lookup+0x425
#10 0xffffffff80c079b8 at namei+0x238
#11 0xffffffff80c2d2da at vn_open_cred+0x53a
#12 0xffffffff80c239a8 at openatfp+0x268
#13 0xffffffff80c236b8 at sys_open+0x28
#14 0xffffffff810011c0 at amd64_syscall+0x100
#15 0xffffffff80fd765b at fast_syscall_common+0xf8

Unfortunately this machine is managed with freebsd-update and has no
swap partition usable for a dump file so my debugging options are a
little limited. I'll see what I can do about that.

There are a number of nfsv4.2 filesystems mounted on this machine, but
knowing that it's related to releasing locks, there are a couple of
potentially relevant factors.

- some (but not all) NFSv4.2 filesystems are mounted oneopenown
- some (but not all) of the NFSV4.2 filesystems are mounted nolockd

Both of those seem like the sort of thing that might lead to releasing
a reference that's already released while releasing an open.

What could I do to debug this further?

Thanks for any advice.