It looks like the AT code shipped by default on the LoRa-E5 module uses the USART1 peripheral on pins PB6 and PB7. However ST’s LoRaWan_End_Node example uses the USART2 which cannot be routed to PB6 and PB7.
Anyone who wants to use LoRaWan_End_Node as the starting point for their LoRaWan project must either re-write LoRaWan_End_Node to use USART1 (this is non-trivial) or else re-wire the Grove-LoRa-E5 to use PA2 and PA3 (which is what I have done).
I would recommend Seeed looks carefully at designs of their boards to ensure that ST’s sample code can run on them with the minimum of software work (and no rework of the hardware). If you were starting again I would recommend wiring the Grove board to use PA2 and PA3 and modify the AT program to use USART2 on these pins.
Anyone who is designing their own PCB should think carefully about which UART pins to use.