Node 151 example code sending empty payloads

I am using the LoRaWAN_151_CC_ADC_v1.1.2 example as my base code. Everything works most of the time, but periodically, it sends and empty payload with no port defined.

“uplink_message”: {
“session_key_id”: “AXvCRdpg7B4KsBHeoYqS6Q==”,
“f_cnt”: 21,
“frm_payload”: “AMeP”,
“decoded_payload”: {},
“rx_metadata”: [

I also see in my debug that it is not getting an ACK on the packet sent

Iteration #42

Measuring BMx Sensor
Into send state
In sending…
Pressure: 97764.03 Pa - 9776403 - 952d13, Temperature: 23.89 C - 2389 - 955
ADC Value : 1281 mv - 501
Battery : 3672 mv - e58
011------------------------

MISSING: 00+SEND:ACK RECEIVED
MISSING: +SEND:DONE

Iteration #43

Waking up. Nothing to do. TxCycleCount = 2

Iteration #44

Measuring BMx Sensor
Into send state
In sending…
Pressure: 97764.59 Pa - 9776459 - 952d4b, Temperature: 23.87 C - 2387 - 953
ADC Value : 1281 mv - 501
Battery : 3672 mv - e58
00+SEND:ACK RECEIVED
+SEND:DONE

The next transmission goes through without issue and the frame counter is still incrementing on TTN.
The weird part is that the code does not attempt a retransmission when it fails to get an ACK.

any help is appreciated,

-michael