We try to avoid RX2 if possible. For RX1 we have 8 channels available, while RX2 is fixed on 1 channel and a very inefficient data rate. Therefore, expect most downlink messages to be sent after 1 second. Losing 400 ms on the slow connection is not ideal, but we can handle it. For now just install the latest packet forwarder from Semtech (GitHub - Lora-net/packet_forwarder: A LoRa packet forwarder is a program running on the host of a LoRa gateway that forwards RF packets receive by the concentrator to a server through a IP/UDP link, and emits RF packets that are sent by the server.) and we’ll make sure the timing on the server side will be better.
In private networks with this issue, you might want to consider increasing the RX_DELAY to (for example) 5 seconds. That would place RX1 at 5 and RX2 at 6, leaving more than enough time for even a satellite backhaul.