Cannot quiesce pfSense (FreeBSD) guest "failed to freeze /: Resource deadlock avoided"

[Gavino]

pfSense 2.8.0 Community Edition is a guest VM and it works well but there is one issue. My backup software cannot quiese the guest before backup. My backup software (Nakivo) says,
"Source host could not create quiesced (application-aware) snapshot of this VM. Reason: Quiescing script was not detected. The VM will be processed without quiescing. This may influence the resulting recovery point reliability."

Within Proxmox VE 8.4 I have the Qemu Agent enabled with:
[tick] Use QEMU Guest Agent
[tick] Run guest-trim after a disk move or VM migration
[tick] Freeze/thaw guest filesystems on backup for consistency
Type: VirtIO

Within the pfSense guest i have the guest agent package installed:

[2.8.0-RELEASE][root@pfsenseTEST.home.arpa]/root: pkg info qemu-guest-agent
qemu-guest-agent-9.1.1
Name           : qemu-guest-agent
Version        : 9.1.1
Installed on   : Thu Aug 28 17:59:42 2025 AEST
Origin         : emulators/qemu
Architecture   : FreeBSD:15:amd64
Prefix         : /usr/local
Categories     : emulators
Licenses       : GPLv2
Maintainer     : bofh@FreeBSD.org
WWW            : https://www.qemu.org/
Comment        : QEMU CPU Emulator (guest agent)
Options        :
        DOCS           : off
        STRIP          : off
Shared Libs required:
        libglib-2.0.so.0
Annotations    :
        FreeBSD_version: 1500029
        build_timestamp: 2025-08-12T17:21:03+00:00
        built_by       : poudriere-git-3.4.99.20250209
        cpe            : cpe:2.3:a:qemu:qemu:9.1.1:::::freebsd15:x64
        flavor         : guestagent
        port_checkout_unclean: no
        port_git_hash  : abeb76805045
        ports_top_checkout_unclean: no
        ports_top_git_hash: d30bcc875fc9
        repo_type      : binary
        repository     : pfSense
Flat size      : 1.63MiB
Description    :
The QEMU Guest Agent is a daemon intended to be run within virtual machines.
It allows the hypervisor host to perform various operations in the guest,
such as:

* get information from the guest
* set the guest's system time
* read/write a file
* sync and freeze the filesystems
* suspend the guest
* reconfigure guest local processors
* set user's password
[2.8.0-RELEASE][root@pfsenseTEST.home.arpa]/root:

It was installed from the simple script here:
https://github.com/Weehooey/pfSense-scripts


From Proxmox I can use the qm guest command to ping the guest, and get network interfaces, and OS info etc. It's just that the freezing and thawing is borked.

root@gtpve01:~# qm guest cmd 666 fsfreeze-status
thawed
root@gtpve01:~# qm guest cmd 666 fsfreeze-freeze
{
   "error" : {
      "class" : "GenericError",
      "desc" : "failed to freeze /: Resource deadlock avoided"
   }
}
root@gtpve01:~# qm guest cmd 666 fsfreeze-status
thawed

Compare that to a Debian 13 install that works for quiescing and backups

root@gtpve03:~# qm guest cmd 103 fsfreeze-freeze
1
root@gtpve03:~# qm guest cmd 103 fsfreeze-status
frozen
root@gtpve03:~# qm guest cmd 103 fsfreeze-thaw
1
root@gtpve03:~# qm guest cmd 103 fsfreeze-status
thawed
root@gtpve03

No Linux or Windows guests that I run on Proxmox have any issues. It's only this one pfSense / FreeBSD host. I have done a fresh install too following the Netgate guide to the letter with all the recommended settings https://docs.netgate.com/pfsense/en/latest/recipes/virtualize-proxmox-ve.html and still no good.

I have tried all kinds of disk controllers and disk formats (raw vs qcow2) but nothing seems to work.

Any ideas where I go from here?

P.S. pfSense backs up fine on VMware ESXi, but that uses the open-vm-tools. I tried installing that too but no good.