@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.
always use the software from the git repository. Do not copy it form the documentation.
Use the latest firmware version with the software from the git repository.
The nanogateway is listening on a single channel only. If you do not configure the node accordingly, the node will send on different channels. The examples for abp_node and otaa_node shoudl cater for that.
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.