This post has become obsolete as it was incorporated in the Welcome to the KPN LoRa forum. An overview
LoRa devices communicate by broadcasting the LoRa signal to every LoRa receiver in the vicinity. The core server collects the messages from all gateways and ignores identical messages and remembers the gateway that had the best reception, e.g. the Last Best Gateway (LBG). For downlink messages, the LBG is selected to act as sender.
For class A devices, LBG is always up to date because the network queues the downlink message to respond shortly after receiving an uplink message. For class C devices, LBG can be outdated if device is moved or environment has changed. A solution could be to send an uplink when a device stopped moving and/or sending an acknowledgment from the device when receiving a message.