While editing the glossary settings, when we try to save form it works fine most of the time but at certain point it throws error.

Debug info: Cannot find grade item for 'glossary'
cm '22' matching number '0'
Error code: err_system
Stack trace:
line 1337 of /lib/completionlib.php: moodle_exception thrown
line 651 of /lib/completionlib.php: call to completion_info->internal_systemerror()
line 584 of /lib/completionlib.php: call to completion_info->internal_get_state()
line 888 of /lib/completionlib.php: call to completion_info->update_state()
line 524 of /course/modlib.php: call to completion_info->reset_all_state()
line 266 of /course/modedit.php: call to update_moduleinfo()