https://devzone.nordicsemi.com/question ... matically/Disconnect Reason 0x003E meant BLE_HCI_CONN_FAILED_TO_BE_ESTABLISHED
https://devzone.nordicsemi.com/question ... ci-errors/ Some more information, reasons for this error.
There is a closed issue with the same error 0x003e https://github.com/espressif/esp-idf/issues/475. He specifies a workaround
Maybe add more debug information like Yulong-espressif suggests in that issue.@jkhax0r Hi, I can connect to nRF51822 by calling esp_ble_gattc_close to close the connection, and then reopen gattc by calling esp_ble_gattc_open. This is not a perfect solution, but it works. If this is a bug, I hope the espressif staff can fix it for a new version of esp-idf.
You are working with a nrf ble device, Try setting up your phone as a GATT Server with nrf connect with matching services/characteristics. This issue could be because of how the nrf ble device works.