There should be an option to select whether the missing/late policy applies to external tool assignments.
An instructor using the New Gradebook sets the Missing Submission Policy to automatically give a zero grade for missing submissions after the due date. A student doesn't submit an assignment which uses an external tool (LTI). The assignment is not marked as missing because it uses an external tool, so the student thinks that their grade is higher than it is and that missing an assignment didn't adversely affect their grade.
The New Gradebook should have an option for the Missing Submission Policy to apply to all assignments consistently-- including external tool assignments.
Possible arguments against this idea:
Although a Support Engineer pointed out it would be problematic to force all external tools to use the missing submission policy because some external tools don't provide an immediate grade, adding an option for it eliminates this argument.
Although instructors can manually set the default score for an assignment, this is a very manual process especially for courses with frequent assignments and there is an unnecessary delay for students to have accurate Grades.
If an instructor goes out of their way to set the Missing Submission Policy to assign zeros for missing assignments, it's counter-intuitive that there's no way for it to apply to external tool assignments. The instructor should have the option for the Missing Submission Policy to apply to all assignments consistently.