@rubencg195 The pull/push ack messaage show the communication via Internet to the TTN server. Independent of that, the LoRa device is always listening, except when it is sending itself. But that would only happen after an uplink message has been send and it was told by the server so deliver a downlink message. It might only happen, that if there are many nodes around sending, then the gateway may have started to listen to another message.
A few notes.
Besides that, I have a comibinatin of a LoPy as nano-gateway and FiPy as nodes running, and they never seem to miss a packet.