I'm trying to use Adafruit IO's CircuitPython library on a Feather M4 Express with the Airlift FeatherWing. I want to be able to use MQTT/IO pub/sub to subscribe to a topic and publish to another topic in a loop, but the mqtt_client.loop() functions seems to block waiting for data to be posted to the subscribed topic once, then the loop call continues as expected. If I don't 'kick' the subscribed topic by publishing data to this topic from the adafruit.io Feeds screen once, the loop() will eventually throw

MMQTTException: Unable to receive 1 bytes within 60 seconds.

I'm using the example code in minimqtt_pub_sub_nonblocking_esp32spi.py (from the latest official v6 release of the CircuitPython IO library) at https://github.com/adafruit/Adafruit_CircuitPython_MiniMQTT/blob/85d9d846f3fd8f9d3ee8ae354c5c34d2e2970c1a/examples/esp32spi/minimqtt_pub_sub_nonblocking_esp32spi.py

while True:
   mqtt_client.loop()
   mqtt_client.publish(topic, value)
   time.sleep(5)

I tried catching and eating the exception, which works intermittently.

while True:
  try:
    mqtt_client.loop()
  except (MQTT.MMQTTException) as e:
    print(e)
  mqtt_client.publish(topic, value)
  time.sleep(5)

Sometimes it'll work (i.e. exception caught, publish works fine, repeat), other times loop() will throw:

Traceback (most recent call last):
File "code.py", line 142, in <module>
File "code.py", line 140, in <module>
File "adafruit_minimqtt/adafruit_minimqtt.py", line 809, in loop
File "adafruit_minimqtt/adafruit_minimqtt.py", line 569, in ping
File "adafruit_esp32spi/adafruit_esp32spi_socket.py", line 82, in send
File "adafruit_esp32spi/adafruit_esp32spi.py", line 721, in socket_write
RuntimeError: Failed to send 2 bytes (sent 0)