Error: received null username or password for unpwd

I can’t get my mqtt to work.

I am on a fresh HASS os installation. This is what I have already done:

Installed the add-on: Mosquitto
Created a new user “mqtt” with password “mqtt”
Installed the service MQTT, did configure and then reconfigure: here I entered username and password “mqtt”

In the log I get:

2024-05-25 18:45:19: New connection from on port 1883.
error: received null username or password for unpwd check
2024-05-25 18:45:19: Client mqttjs_c1f836a6 disconnected, not authorised.

What’s wrong here?

I am quite positive it is a bug. No other mqtt client can login. I have created also users with longer names already. It will always say that there was no password or username received. Which is wrong.