If your RUI3 version is RUI3 V4.2.1 (you can check with AT+VER command) the LoRaWAN stack version is V1.0.4 and for the regional parameters select RP002-1.0.4
For the failed sending, I have only the explanation of Duty Cycle problems.
I have multiple RUI3 based air quality sensors running for months, sending data every 5 minutes, without any problems. But I am using AS923-3, which allows me to override the Duty Cycle.