Manage Classes Issues

Hi everyone I am new in Opigno I have a 2.15 and I have a issue when I try the see the Classes Stadistics in this path group/classes When I try to see any class I see this Message I try to restore again but is the same issues and also update the drupal Drupal core 8.9.6 but continue equal InvalidArgumentException: The timestamp must be numeric. in Drupal\Component\Datetime\DateTimePlus::createFromTimestamp() (line 201 of core/lib/Drupal/Component/Datetime/DateTimePlus.php). somebody can helpme please regards