Packet loss issue with increased range

Even if in between trees, it seems strange that you have such a poor SNR (this is what I obtain at 3km with an indoor gateway, 10m above the ground…). I would try to test the connection at the same distance but in a clear area (or putting the node at some height on the trees), but also check what @cslorabox is suggesting regarding antennas and connections (including shortening the payload…).