Thank you for the hint with the later uplink + acknowledge.
I found out that the acknowledge flag is only send in the next message if I send a second message without setting the module to sleep, which I do for longer intervals and re-init at boot-up. But if it sends the next message with the acknowledge flag, the console interprets that correctly, shows the acknowledge (see screenshot) and stops the confirmed download.
Message 3715 triggers the downlink but until 3716 the module goes to sleep and is re-booted, so 3716 doesn’t bring an acknowledge with it and the download is triggered again. There is no re-boot between 3716 and 3717, and the message 3717 contains the acknowledge flag.
But as you said, the empty message for pure acknowledging could be the problem. Maybe that is fixed in V3 stack? If anyone know, please share that information.
As I said, and it showed valuable, that I wanted to test this process.
In the product I need this only on very few occasions, where I download a configuration to the node and I want to make sure that the configuration that I set e.g. in a mobile app is really received by the node. The configuration can later be viewed in the mobile app and needs to be trusted.