ESPresense sensor remains off-line

Configuration
1

Adding a new ESPresense sensor to an existing setup fails to be detected by Home Assistant and MQTT Explorer reports that Status as Off-line.

Configured (multiple) new ESP32-WROOM-32 board with a identical configuration as the existing (and still working) ESP32 sensor.
The ESPresense device operates correctly, and I can see the Fingerprints it finds.

In MQTT Explorer, the existing sensor in /rooms/shed is working prefectly, while the new sensor in /rooms/studyroom/status = offline. This status refreshes every 6 seconds. So I can deduce that MQTT credentials have been accepted and are seen in Home Assistant.

I am at a loss to understand why MQTT receives a offline status from the ESP32-WROOM-32, presumably, this explains why Home Assistant does not discover it?

Any thought as to what is going on and how to overcome?

Screenshot 2024-08-01 175636
Screenshot 2024-08-01 1756361247×353 28.9 KB

Screenshot 2024-08-02 092212
Screenshot 2024-08-02 0922122000×1403 284 KB

2

Found the issue, not a solution.

My goal to is have an expanded subnet to cope with increasing number of devices.

In preparation for a 100 new Wi-Fi down-lights, I changed the Network subset mask on my Asus RT-AC66U router.

The Network address is 192.168.0.0 and the Default subnet mask is 255.255.255.0(253 devices 192.168.0.1 to 192.168.0.254)

When I changed the subnet mask to 255.255.240.0 (4K devices between 192.168.0.1 to 192.168.15.254) AND the router assigns an address outside the Default range, MQTT Explorer reports it offline.

When the subnet mask is changed back to the Default and restart - MQTT Explorer reports it status is on-line.

This behaviour seem that the Espresense sensor presumes it will be assigned using Default subnet mask before it signals that it is online?

any ideas how to overcome?