I have found why the Support System was not sending email to the administrator when a ticket was created.
It has to do with the slug. You should look into this because it can create problems.
The Support System uses "Main Administrator", its slug in order to notify of a new ticket as instructed with "If the ticket is not assigned to any staff member, This will be the Administrator who receives all emails with any updates about the ticket".
The problem that I had is that the Support System picked up a previously created slug (I had previously use the Edit Author Slug plugin) and not the current one. Apparently it couldn't find a matching email for that slug.
After revising the slugs, re-installing Edit Author Slug and selecting another slug for the Support System, it worked.