Sodaq Mbili and Rn2483:Failed to send packet


I’m using the Sodaq Mbili with the RN2483 module.
Now I have a sensor connected to the Sodaq and with Arduino I programmed to get data from it and send it over by LoRa to All things Talk. Now I’m having the issue that my messages are send to and received in my All Things Talk dashboard but the serial monitor from my Arduino says:
Failed to send packet.
Sometimes it also displays:
[lookupMacTransmitError]: mac_err
[lookupMacTransmitError]: found 3.

Does anyone know what it could be or have any experience with these?

I don’t understand why it’s telling me on the serial monitor that it failed but that I that in reality the message is mostly send, it happens only a few times that the message is really not send.