Problems that have not been solved before,

[strengthstrong]

https://devzone.nordicsemi.com/f/nordic-q-a/9231/ble_hci_conn_failed_to_be_established-0x3e-problem/34074#34074

I also encountered the same problem as this one. How to solve this problem in the end, this question did not answer at the end.

[Hung Bui]

Hi,

Please give us some more information about your setup, which devices you used, which softdevice, SDK, how you tested. 

The BLE_HCI_CONN_FAILED_TO_BE_ESTABLISHED error usually happens when the connect request from the central isn't received by the peripheral and the peripheral doesn't response after the next  6 empty PDU. 

[strengthstrong]

https://devzone.nordicsemi.com/f/nordic-q-a/35855/immediately-after-the-connection-is-established-the-connection-0x3e-is-disconnected-after-several-connections-the-connection-is-not-broken-occasionally-the-connection-is-disconnected-after-the-connection-is-established-0x08  

[strengthstrong]

I use the sdk14.2 nrf52832 as the primary end, the two iphone phones as slaves, to establish a connection in most cases because of the 0x3e error to connect several times in order to maintain the connection, almost no disconnect after the connection is maintained, I think it possible There is a problem when you just started to establish a connection.