Cayenne Payload Size Problem

I have a Heltec ESP32 LoRa board with OLED version 2.
It has been working well but I wanted to start using the CayenneLPP library to encode the payload.
It is working but I am having a problem.

Using OTAA, the board joins fine and sends the first payload (4 sensor values), these are delivered and decoded with no problems. Subsequent payloads appear in the Device Data tab, but there is never any payload.
I have noticed that when I reduce the payload to only 2 sensor values, every payload is delivered and decoded properly. Anything over 2 values has the same problem of succeeding the first time, but failing for future readings.

When I turn on the debugging serial readout on the device, it shows a “DIO1: RX timeout” error for unsuccessful packets. Is this something that can be addressed within Chiprstack, or does this sound like a hardware, or gateway problem?