Looking for help

I am looking for help. I am looking for help in terms of a person. I am trying to develop a software/gateway platform using Raspberry Pi and a LoRa concentrator using SX1308 chips.
The plan is to have a gateway connecting to LoRa nodes with Web Interface and additional feature set. While having said that, there is no plan for upload to TTN or with MQTT otherwise.
Many things are working already. But I am stuck with the Join Request and Accept using OTAA. I can validate MICs, but at the end of the day it seems SX1308 is not sending out anything.
USB Consoles of my LoRa nodes just keep on sending out Join Messages. There is no Error or something similar. I tried to hit the receive windows with different timings and I also set the Nodes for permanent listening through giving them Class C.
I also connected my Raspberry Pi to TTN using Semtechs Packet forwarder. There I see join requests as well and TTN sending Join Accepts. But never ever had sensor values in TTN.
So my primary questions are What am I doing wrong and/or Is my Concentrator defect? Great help would be
a.) a program that sends and on other radio it receives its own message
b.) a LoRa node with USB console being more verbose
c.) Any other ideas.