LoRaWan Gateway Kit 868MHZ - Problem with Class B mode

I recently purchased the following LoRaWAN Gateway Kit:

I performed several tests with this kit and I also installed within the Raspberry PI 3 the ChirpStack open-source LoRaWAN Network Server stack.
One of my goals is to test the LoRaWAN Class B mode with some end nodes.
Obviously, I connected the Raspberry PI 3 to a GPS module and I also connected the PPS output to the pin 24 of the RHF0M301 module.
If I use the packet forwarder binary provided within the SD card of the Raspberry PI 3, the end nodes are able to switch into Class B mode and to set up ping slots correctly.
I tested this behaviour by installing the I-CUBE-LRWAN library (v1.3.1) and the LoRaMac-node stack implementation within the end nodes.

However, If I use the packet forwarders provided by RisingHF (https://github.com/risinghf/packet_forwarder) or the Lora-net packet forwarder the end nodes are no longer able to switch into Class B mode despite the beacons are sent by the gateway.

This problem occurs with the Class B mode; for what concerns the Class A mode the communication between end nodes and the Network Server is ok.
I would add that the configuration of the ChirpStack Network Server and the global_conf.json files are ok.
As end nodes, I use the following boards/kit:

  • STM32L0 B-L072Z-LRWAN1
  • STM32L476RG with LR1110

Obviously, I downloaded from GitHub the packet forwarder source releases that I found within the SD card of the Raspberry PI 3 (lora-gateway v4.0.1 - packet forwarder v3.0.0).

What could be the problem of this strange behaviour about the Class B mode if I use the packet forwarder sources?
Waiting for your reply.
Thanks in advance.

Best regards