After the completion of a tracked activity you can launch a new attempt.
While x.start.time correctly tracks the starting of a new attempt, everything related to the datamodel will be assigned to the first attempt (attempt = 1) 'cause of a typo in accessing the session variable charged to store the attempt number.
1. Creation of the session scope, mod/scorm/player.php:

...

    $SESSION->scorm_attempt = $attempt;

...

2. Accessing the session scope missing the prefix "scorm_", mod/scorm/aicc.php:

...

        if (isset($SESSION->attempt)) {

            $attempt = $SESSION->attempt;

        } else {

            $attempt = 1;

        }

...