When accessing the "Activity completion" report, a DB error is displayed.

It seems because the SQL query that is generated repeats the "u.idnumber" field.

It might happen when the user's idnumber field is defined at the environment level in showuseridentity.

It has worked for us to change the line:

File : ./lib/completionlib.php
Function: get_tracked_users()

Line :
$sql = 'SELECT u.id, u.idnumber ' . $all usernames;
by
$sql = 'SELECT u.id ' . $all usernames;

Note: DB is Oracle.