I just wanted to publish the solution given by the support team (yay!), which is very similar to the one that Nika_Hadzhikidi proposed (thank you Nika!):
1- In CSA, under Reporting, create a new organization and update the username with superuser. (not sure why it has to be superuser here, but it actually works)
2- Run the command to create the keystore.
admin jasper keystore
and copy files...
3- Delete previous organization in Jaspersoft.
4- admin content-jaspersoft csk –userName superuser -password superuser
5- Create and Update Jaspersoft Users... job
And... that's it, this time I had my users created in Jaspersoft since step 4, and in step 5 all my users with the Advaced Reporting rights were sync'ed
As a hint... I remember that during my first configuration, in step 4 I didn't see my users being created in Jasper... so maybe at that point it's better to follow the previous steps.