Enabling watchdog causes systemd to hang at reboot on rPi5

[marcmerlin]

G_DIETPI_VERSION_CORE=9
G_DIETPI_VERSION_SUB=12
G_DIETPI_VERSION_RC=1
G_GITBRANCH=‘master’
G_GITOWNER=‘MichaIng’
Linux aragorn 6.12.25+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.12.25-1+rpt1 (2025-04-30) aarch64 GNU/Linux
arm64

perplexed about this, I installed watchdog on dietpi, I even tried this

aragorn:~# dpkg --status watchdog
Package: watchdog
Version: 5.16-2~rpt2
(...)

aragorn:~# cat /etc/systemd/system/watchdog.service.d/override.conf
[Unit]
Conflicts=reboot.target shutdown.target

reboot shows this on serial

[  OK  ] Removed slice system-modpr…lice - Slice /system/modprobe.
[  OK  ] Stopped target bluetooth.target - Bluetooth Support.
[  OK  ] Stopped target graphical.target - Graphical Interface.
[  OK  ] Stopped target rpcbind.target - RPC Port Mapper.
[  OK  ] Stopped target timers.target - Timer Units.
[  OK  ] Stopped dpkg-db-backup.tim… Daily dpkg database backup timer.
[  OK  ] Stopped fstrim.timer - Discard unused blocks once a week.
[  OK  ] Stopped logrotate.timer - Daily rotation of log files.
[  OK  ] Stopped systemd-tmpfiles-c… Cleanup of Temporary Directories.
[  OK  ] Stopped target time-set.target - System Time Set.
[  OK  ] Closed systemd-rfkill.sock…l Switch Status /dev/rfkill Watch.
         Unmounting mnt-btrfs_boot.mount - /mnt/btrfs_boot...
         Unmounting mnt-firmware2.mount - /mnt/firmware2...
         Unmounting mnt-sdcard.mount - /mnt/sdcard...
         Unmounting mnt-sdcard_boot.mount - /mnt/sdcard_boot...
         Starting dietpi-kill_ssh.s…m - DietPi-Kill_SSH on shutdown...
         Stopping nfs-blkmap.servic…NFS block layout mapping daemon...
         Stopping nfs-server.service - NFS server and services...
         Stopping systemd-random-se…ice - Load/Save Random Seed...
         Stopping watchdog.service - watchdog daemon...     <<<<<<<< stopped hereh
[  OK  ] Stopped nfs-blkmap.service… pNFS block layout mapping daemon.
[  OK  ] Stopped ssh.service - OpenBSD Secure Shell server.
[  OK  ] Unmounted mnt-btrfs_boot.mount - /mnt/btrfs_boot.
[  OK  ] Unmounted mnt-firmware2.mount - /mnt/firmware2.
[  OK  ] Unmounted mnt-sdcard.mount - /mnt/sdcard

but then it hangs, no reboot unless I use sysrq+b
and if I just do
reboot is aliased to `/etc/init.d/watchdog stop; \reboot’
and then reboot works fine, 100%

Any idea what’s going on?