MQTT-TLS library on Argon: not connecting to broker

Hi I am using the MQTT-TLS library on my Argon 4.0.2, I have previously used this library successfully by flashing it on an Argon with device OS 4.0.2, to connect to a secured broker with username, password and provided CA certificate.
Now I would like to replicate on another Argon in which I have restored the 4.0.2 version of the device OS.
Using the workbench, I can flash the project including the MQTT-TLS library and test it with the on the secured port 8883. I can publish and subscribe so I would say that everything works. However, if I connect to another secured broker I can never connect, I am sure about this also because I've set the D7 pin to turn on when client.isConnected() is true. Do you have any clue on what may be wrong? I am sure to not have changed anything from the previous project in which I was connecting to the same broker.

What changes to the server are you making?
Nothing should have changed recently. If it's working on the test server, it should work everywhere.