I remember when installed the theme, in my dashboard some statistics and notifications appear, but now the dashboard is empty. I imagine that disabled (unintentionally) this function.
How can I enable the statistics and notifications again?
When you switch themes (child themes), the dashboard plugin automatically gets deactivated. Once deactivated all the widgets are removed from the Instructor/Student sidebar. You'll need to re-add them in the sidebars. Follow this tutorial : https://wplms.io/support/knowledge-base/wplms-dashboards/