Node-red, lost UDP frames

Hello,

I use Node-red on the Multitech Conduit, to make an UDP connection with my server.
The Node-Red is used to transfert LoRa frames to UDP connection.

I use the UDP input node on the 56000 port in ipv4 and the UDP output node on the 5683 port in ipv4.

When Node-red send a message to the UDP output node I have no problem.

But sometimes when my server send message to the UDP input, the message just disappear.
I check with tcpdump on this UDP port, all the messages appear on it but not all of them arrive at the node-red (I check on the debug print and on the LoRa log).

Is anyone have a track to determine why those UDP frame disappear and how correct it?

Regards,
Carole