Attention Serious Failure DataBase Account..
I swapped my WHMCS 7.9.1 from one Account Dominio.site to Another Account Dominio.eu. I was surprised to realize that WHMCS has always been working with a database from the first domain, I forgot to change.
Finding out a while later when deleting databases on the first domain ... strange, never gave a domain error on whmcs 7.9.1.