That is not a frequency used by TTN in the “North America (902-928 Mhz)” band you said you are trying to use.
To see the actual frequencies used, look at: https://www.thethingsnetwork.org/docs/lorawan/frequency-plans.html
Both your gateway and your node will need to be configured to use correct frequencies.
Yes, the end-node and gateways are less than 10 meters. I don’t believe that is the problem because when I use Xplained Pro, it joins correctly. Only with the node I developed the problem appears randomly.
Random success/failure is exactly what would tend to result from overload.
Though of course that is not the only thing that could be causing it.