Notifications don’t work if you compiled your sketch using one of the Blynk 1.0.0-Beta.x libraries, could that the cause for your rogue device?
The notify API call requires the message to be in the body, and I’ve not found a simple way to do that via a simple browser call - but I’ve only tinkered with it a little.
Your real solution is not to run any Blynk code on your devices at all, and install Node-Red on a device on your network and use the Blynk plugin for Node-Red as a bridge between Blynk and MQTT.
This is how I use Blynk and it’s far simpler, more flexible and more robust than any other way of combining Blynk and MQTT.
The Notify node for Blynk in Node-Red simply passes the MQTT payload to Blynk and this arrives as the notification a fraction of a second later.
This is my Node-Red flow for sending me an notification when someone presses my doorbell…
The doorbell sends an MQTT message on the “UK/Doorbell_Alerter/Doorbell_Pressed” topic and the current time is appended to this and passed to the Notify node, which sends the notification. The limit node ensures that I don’t get more than one notification every 5 seconds if someone gets a bit overenthusiastic with the button.
More on some of my HA stuff here…
Pete.