Hi Micheal,
The nature of LoRa communication is such that there is no guarantee that a down link or up link packet will be received on the other side. You can enable acknowledgements and link checks improve odds of delivery but at a cost. Reading the following link may help shed light on the matter.
http://www.multitech.net/developer/software/lora/introduction-to-lora/
The receive window I am talking about is the window that is used by the mDot to receive down link packets from the network server following an up link.
Kind regards,
Leon