Firebeetle Cover-LoRa

I have designed a Water Quality Buoy with about 9 sensors, all of them dfrobot. I've had a lot of trouble with the sensors as most are 5V and the firebeetle is 3.3. I've used Logic Level Shifters for some of the sensors but 2 sensors refuse to play ball. I presume there is some hard coded 5V values in the libraries. The 2 sensors are the ORP and Dissolved Oxygen sensors. So I had the idea of connecting these 2 sensors to a Nano and then using Serial2.print to send them to the ESP32. This works well until I try and connect to the TTN. I get an accept join-request & Successfully processed join-request but no data is passed to TTN. Data does pass to TTN using the same program as long as the Nano isn't connected to 16 & 17 for the Serial2.print.

My question is why is this happening and is there any way around it?