on every kernel that i use i have often messages that watchdog did not stop with shutting down computer. i found two working workaround to fix this problem so maybe in future someone use this for fix:

first solution:
sudo nano /etc/systemd/system.conf
find this text:

#RuntimeWatchdogSec=0
#ShutdownWatchdogSec=10min

and replace

RuntimeWatchdogSec=0
ShutdownWatchdogSec=0

or second solution blacklist modules that hanging system at boot and shutdown

sudo nano /etc/modprobe.d/watchdog.conf
blacklist acquirewdt
blacklist advantechwdt
blacklist alim1535_wdt
blacklist alim7101_wdt
blacklist booke_wdt
blacklist cpu5wdt/etc/udev/rules.d/70-wifi-powersave.rules
blacklist eurotechwdt
blacklist i6300esb
blacklist i8xx_tco
blacklist ib700wdt
blacklist ibmasr
blacklist indydog
blacklist iTCO_wdt
blacklist it8712f_wdt
blacklist it87_wdt
blacklist ixp2000_wdt
blacklist ixp4xx_wdt
blacklist machzwd
blacklist mixcomwd
blacklist mpc8xx_wdt
blacklist mpcore_wdt
blacklist mv64x60_wdt
blacklist pc87413_wdt
blacklist pcwd
blacklist pcwd_pci
blacklist pcwd_usb
blacklist s3c2410_wdt
blacklist sa1100_wdt
blacklist sbc60xxwdt
blacklist sbc7240_wdt
blacklist sb8360
blacklist sc1200wdt
blacklist sc520_wdt
blacklist sch311_wdt
blacklist scx200_wdt
blacklist shwdt
blacklist smsc37b787_wdt
blacklist softdog
blacklist twl4030_wdt
blacklist w83627hf_wdt
blacklist w83697hf_wdt
blacklist w83697ug_wdt
blacklist w83877f_wdt
blacklist w83977f_wdt
blacklist wafer5823wdt
blacklist wdt
blacklist wdt_pci
blacklist wm8350_wdt

both method tested and repair hanging watchdog