connection stuck after disconnection

I use echo example to set our BLE module as peripheral and use "nRF Connect" App of Nexus 7 2013 and iPhone 6 to connect the BLE module.

I can rapid connect it successfully firstly, but the 2nd connection will be stuck when I try connect it again after I disconnect the first connection.

There are no any log, just connection stuck unless I use ctrl+c to interrupt and then reset the "echo example".