Hi @itacos !
You are seeing the packet loss, beacuse in that case the node is trying to use the other base channels (frequencies: 868.3 & 868.5 MHz). Which you can’t disable using the lmic lib in this manner. I faced this issue aswell.
The only way is to modify the base channels/frequencies in the lib (lorabase.h, EU868_F2&F3).
For the rest of channels/frequencies (3-8) you probably can manipulate this using LMIC_setupChannel command.
We all now that this could violate the frequency usage (1%), and is not lorawan compliant, so shall careful doing so!