Proxmox VE 8.4.16 - All LXCs fail to start after Proxmox update

[NickSki]

Just did a regular update of my Proxmox that's been running fine for 18 months.
Now none of the LXCs will start - none of my live LXCs or Test LXcs start - they all fail in a similar way.

I'd appreciate any help offered as I'm totally stuck.
I've pasted the output from a basic debug start below.

Thanks in advance ... Nick

run_buffer: 571 Script exited with status 32
lxc_init: 845 Failed to run lxc.hook.pre-start for container "100"
__lxc_start: 2034 Failed to initialize container "100"

TASK ERROR: startup for container '100' failed

 lxc-start -n 100 -F -lDEBUG -o lxc-100.log:

lxc-start 100 20260117174036.944 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type u nsid 0 hostid 100000 range 1000
lxc-start 100 20260117174036.961 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type g nsid 0 hostid 100000 range 1000
lxc-start 100 20260117174036.964 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type u nsid 1000 hostid 1000 range 16
lxc-start 100 20260117174036.966 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type g nsid 1000 hostid 1000 range 1
lxc-start 100 20260117174036.968 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type u nsid 1016 hostid 101016 range 64520
lxc-start 100 20260117174036.970 INFO     confile - ../src/lxc/confile.c:set_config_idmaps:2273 - Read uid map: type g nsid 1001 hostid 101001 range 64535
lxc-start 100 20260117174036.115 INFO     lsm - ../src/lxc/lsm/lsm.c:lsm_init_static:38 - Initialized LSM security driver AppArmor
lxc-start 100 20260117174036.118 INFO     utils - ../src/lxc/utils.c:run_script_argv:587 - Executing script "/usr/share/lxc/hooks/lxc-pve-prestart-hook" for container "100", config section "lxc"
lxc-start 100 20260117174036.342 DEBUG    utils - ../src/lxc/utils.c:run_buffer:560 - Script exec /usr/share/lxc/hooks/lxc-pve-prestart-hook 100 lxc pre-start produced output: mount: /var/lib/lxc/.pve-staged-mou>
       dmesg(1) may have more information after failed mount system call.

lxc-start 100 20260117174036.342 DEBUG    utils - ../src/lxc/utils.c:run_buffer:560 - Script exec /usr/share/lxc/hooks/lxc-pve-prestart-hook 100 lxc pre-start produced output: command 'mount /dev/dm-6 /var/lib/l>

lxc-start 100 20260117174036.348 ERROR    utils - ../src/lxc/utils.c:run_buffer:571 - Script exited with status 32
lxc-start 100 20260117174036.348 ERROR    start - ../src/lxc/start.c:lxc_init:845 - Failed to run lxc.hook.pre-start for container "100"
lxc-start 100 20260117174036.348 ERROR    start - ../src/lxc/start.c:__lxc_start:2034 - Failed to initialize container "100"
lxc-start 100 20260117174036.348 INFO     utils - ../src/lxc/utils.c:run_script_argv:587 - Executing script "/usr/share/lxcfs/lxc.reboot.hook" for container "100", config section "lxc"
lxc-start 100 20260117174036.850 INFO     utils - ../src/lxc/utils.c:run_script_argv:587 - Executing script "/usr/share/lxc/hooks/lxc-pve-poststop-hook" for container "100", config section "lxc"
lxc-start 100 20260117174037.102 DEBUG    utils - ../src/lxc/utils.c:run_buffer:560 - Script exec /usr/share/lxc/hooks/lxc-pve-poststop-hook 100 lxc post-stop produced output: umount: /var/lib/lxc/100/rootfs: no>
command 'umount --recursive -- /var/lib/lxc/100/rootfs' failed: exit code 1

lxc-start 100 20260117174037.108 ERROR    utils - ../src/lxc/utils.c:run_buffer:571 - Script exited with status 1
lxc-start 100 20260117174037.108 ERROR    start - ../src/lxc/start.c:lxc_end:986 - Failed to run lxc.hook.post-stop for container "100"
lxc-start 100 20260117174037.108 ERROR    lxc_start - ../src/lxc/tools/lxc_start.c:lxc_start_main:307 - The container failed to start
lxc-start 100 20260117174037.108 ERROR    lxc_start - ../src/lxc/tools/lxc_start.c:lxc_start_main:312 - Additional information can be obtained by setting the --logfile and --logpriority options