I am quite bad with ST software team as well. Especially, almost of software examples are not aligned with STM32CubeMX which is ST promoted way to work with their MCU products.
For those who may have problems with DevEUI, you may try create a new firmware based on ST latest example (version 2). At least, it works for my STEVAL board with my country LoRaWAN provider. I am using Keil with free license for STM32L0 processors (http://www2.keil.com/stmicroelectronics-stm32/mdk). You can modify network settings in the following file. Please note that the key factor is to enable STATIC_DEVICE_EUI setting that allow you to set your own DevEUI.
STM32CubeFunctionPack_LORA1_V2.0.1\Projects\STEVAL-STRKT01\Applications\LoRa\Asset_Tracker\LoRaWAN\App\inc\Commissioning.h
#define OVER_THE_AIR_ACTIVATION 1
#define LORAWAN_PUBLIC_NETWORK true
#define STATIC_DEVICE_EUI 1
#define LORAWAN_DEVICE_EUI { 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x?? }
#define LORAWAN_JOIN_EUI { 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x?? }
#define LORAWAN_APP_KEY { 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x?? }
#define LORAWAN_NWK_KEY { 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x??, 0x?? }