We have created a customer by WebAPi, we receive a response and the record is available in the database. The record doesn't appear in the Magento backend.
We did another test by creating an account on the front-end. When this customer is saved it is in table 'customer_entity' , but not visible in the Magento backend.
Refreshing cache doesn't help.
Magento 2.1.1. default install
PHP 5.6.16
MySQL 5.7.9