Unable to put MQTT client into a subsidiary thread

[rpgoldman]

I have some code that successfully subscribes to an MQTT broker, and that logs messages to the screen, using as:start-event-loop.

But since this takes over everything, I wanted to run the event loop in a secondary thread. I put the call to as:start-event-loop into a call to bordeaux-threads:make-thread. But now, when I try to run that code, I get a constant stream of warning messages like this:

WARNING:
   MQTT error: Timed out writing message: #S(CL-MQTT::MQTT-MESSAGE
                                             :FIXED-HEADER 192
                                             :PROTOCOL-NAME ""
                                             :PROTOCOL-LEVEL 0
                                             :CONNECT-FLAGS 0
                                             :CONNECT-KEEPALIVE 0
                                             :RET-CODE-RAW 0
                                             :CLIENT-ID ""
                                             :MID 0
                                             :TOPIC ""
                                             :WILL-TOPIC ""
                                             :WILL-MESSAGE ""
                                             :USERNAME ""
                                             :PASSWORD ""
                                             :PAYLOAD #()
                                             :SUBSCRIPTION-QOS-RAW 0)

and no logging messages are ever printed. My understanding is that it should be possible to run the cl-async event loop in a thread. I don't understand what it is about an MQTT client that would make running in a thread different from running in the main process. It seems that somehow a timeout is being triggered, but the client code does not set a timeout anywhere.