Unable to select a task as a non-admin user

Good morning,

We have an interface which queries the tasks from the user logged in thanks to a task user report. If we use an admin user, we are able to see all these tasks (group and individual), but if we use a test user without admin privileges, we are unable to see them.

In the report, if we set the context user to the test user, we can see the tasks, so we don't think is a report issue.

Thank you so much