Hello John
The watchdog timer is used to monitor the status of a component. It operates by monitoring responses. When it stops getting a heartbeat from a component that it is monitoring then the timer expires, and you receive an error in the log. When the timer expires it will initiate whatever action is set. If the operating system stops responding then the timer will expire and restart the server if it is set to perform that action.
The above error doesn't tell us why the timer expired, so you will need to review your hardware and operating system logs to find out what happened when the timer expired.
Thanks