If a module's edit_form.php throws an exception due to some sort of configuration requirement (or any other reason for that matter) it causes the defaultcompletion.php to break as the exception does not get handled in this case. 

Throwing an exception is is suitable for the add/edit form, but not on this "sub-form" page.

The default activity completion page also assumes that plugins have implemented mod_form.php (which it should, but isn't actually checked as part of a plugin's validity), and if any module happens to fail to check this, the whole page fails (instead of just that module's part).

This failure could be handled both here as well as an update to plugin QA checking.

Since the page is already removing plugins fail to implement the suffixing, other failures should be similarly handled, rather than resulting a "catastrophic" failure of the entire page.