Create refernce to change table from change order workflow task message template
OOTb message template sends blank mail notifications.
CA Service Desk Manager, all releases
Any reference to change table from templates has to be made with reference on "chg".
In OOTB message template refernce is made using "Change_id".So edit the template and change "Change_id" to "chg"
And also for OOTB Change Workflow template there is no HTML message.
If needed copy complete HTML message from any of the OOTB Change Template to this Change WF template and modify the reference to change table as "Chg".
Below is the screenshot after making the reference changes to template: