Open a process which contains a human task (assigned to a group)
Double-click on the task to bring up the human task editor.
Just make some changes, click OK.
Save the process.
Now the task's group allocation is gone
In the jbpm5 eclipse plugin, while I open and save the human task editor of a task which already has some value like groupid, result mapping, etc.., the save operation removes the groupId from the task.