QMqttConnection::ensureTransportOpen can't use correctly a secure socket in the connected state

This bug is similar to QTBUG-66955 but it happens when trying to use a valid and connected secure socket, e.g.:

p_mqttClient->setTransport(secureSocket, QMqttClient::SecureSocket).

As a workaround, you can use the following instead:

p_mqttClient->setTransport(secureSocket, QMqttClient::AbstractSocket)