We are the developers of Wooclap, an activity plugin where students can answers real-time interactive questions during a live course and the teacher can synchronize their results in the course Gradebook after the course.

Upon synchronization, we observe an error in the Gradebook where sometimes our activity appears multiple times (over multiple columns), instead of one column per activity as expected.

Visual illustration from our test environment (on Moodle 3.9):

To synchronize the grades, following the Grades documentation, our plugin uses the grade_update function which is called once for each user.

Here are the two function calls that produces the result above:

grade_update(
  'mod/wooclap',
   2, // id of the course
   'mod',
   'wooclap',
   21, // id of the activity
   0,
   ['userid' => 2, 'rawgrade' => 100],
   ['itemname' => 'columns 3']
);

grade_update(
   'mod/wooclap',
   2, // id of the course
   'mod',
   'wooclap',
   21, // id of the activity
   0,
   ['userid' => 3, 'rawgrade' => 0],
   ['itemname' => 'columns 3']
);

Both return a GRADE_UPDATE_OK (=0) response.

I would expect those two calls to update different cells of a same column in the Gradebook instead. What could cause two different columns to be created? Is there something I'm not understanding correctly?

Note: Not sure if relevant to this bug, but running the synchronization again (so re-running the function calls above) return a GRADE_UPDATE_MULTIPLE error.

Thanks in advance for your help on this issue.