MQTT unrecognized client

Configuration
1

I am setting up MQTT (Mosquitto broker) and looking in the add-on log I find a problem or concern, which is an unknown (to me) client connecting then closing:

ddtt New connection from 172.30.32.2:53466 on port 1883.
ddtt Client closed its connection.

all of my devices are in a 192.168.1.xx subnet, not 172…

Does anyone know how to track down what this is?

2

I found the answer after posting, of course.