Strange behavior of one ESP32 device. It becomes invisible. Any ideas?

Hi!
I have reworked my simple clock to work with MQTT server. It is not so simple now :)
It gets additional fields to display from MQTT server, while a few devices send data to the server and JS agent works on the server and converts incoming data from the sensors to data for clock.
One of the sensors is a controller of very small greenhouse. It measures temperature, turns on and off heating and light and sends its state to MQTT server. It is ESP32 board. (I put it in place of old MSP32-based controller because the old one has no wireless communications).
Everything works. But the controller becomes invisible to other devices on my local network in a small period after power on. I can connect to it and can ping it from MQTT server but not from any other devices.
I've captured some packets in my network using tcpdump and have found that the controller does not answer to ARP requests. I can not check if it receives the requests.
I have a few other ESP32 devices with the same version of Espruino (v2.00) and they are visible. One possible difference is that the controller is at longest distance (RSSI is usually about -85).
It looks strange, while is not a problem. Why it may be?