How do you send the data? Are you using the cli for that or using another library to send data to the local broker?
cli: There is a --qos command which you could set to 2.
Other library: The topics are bridged via qos 2, such that as soon as you made sure the payload was send to the local broker (e.g. via sending with qos 2) the data will be send to cumulocity with qos 2 as well.
QOS is quality standard and it is the contract between Edge and Cloud
Message failures can also occur once after the message is reached to the cloud.
In this scenario our custom code in edge persists all failures and and should retry until message is successfully stored in cloud
Therefore against each published telemetry (D2C) message,there must be acknowldgement(C2D) to ensure the cloud has accepted message without any systeam or cloud component crash internally
And Assuring QoS implementation does not always gurantee Successful delivery of messages