"Authorization failed or requested resource not found" on almost all admin screens

Summary:

• Almost all of admin screens returns messages either;
  • "Authorization failed or requested resource not found" or
  • "You don’t have permission to view these resources in this compartment".

Content (required):

Almost all of admin screens returns either of the messages above, and I cannot control any resources.

Also, at least one screen goes to blank. (when I hit "Add a user to your tenancy" below "User Management" in the right pane on the home screen)

I was going through the training course "Oracle Cloud Infrastructure Foundations" to "Hands-on Activity: Compute", and the next day I fell this situation. I have completely lost any control to my tenancy since then.