Hi Luigi,
I just tested your flow, setting the connection to my own local broker. Works exactly as it should. Have you tested the connection itself to your broker without node-red? For example by using a tool like MQTT Explorer?
MQTT Explorer v0.2.0 - MQTT swiss-army-knife
Setting up a connection in advanced mode should allow you to connect with TLS and local certificates with it. See if you can get it there to work first. if you press the inject button in Node-RED, you should see it appear in
Scratch that, I'm seeing in your opening post that you can already see it in the service cockpit... Based on those combinations and what I'm seeing here it should work, especially as your MQTT nodes show as connected.
Your flow shows that you have a folder on your desktop that is called Desktop. Is that folder indeed there? Take a look at the following reported issue on the MQTT core node and see if it applies to your situation, that would explain what you're seeing: https://github.com/node-red/node-red/issues/1960
It uses the following path: C:\Users\lalboino\Desktop\Desktop\Progetti_finanziati_regione_Puglia\Device_Predictive_DF_ARIMA_NEW\Predictive_DF_Arima_New-device_certificate_chain.pem
Where C:\Users\<name>\Desktop is the normal path on Windows installations for the user's Desktop, so an additional Desktop in the path is something I notice 
In the meantime mentioning @knolleary for a potential bug as that issue never got responded to.
