Transmit status goes to 0x25 - route not found

I’m sending out packets, in API mode, with a small amount of data. I’m doing this in a loop ( maybe 20 times ). About the 12th time, the delivery status goes to route not found. Any idea on why the status changed and what I can do to prevent this? Thanks.

Personally, I think because you transmitted data in 20 times, packet maybe drop. The source therefore didn’t receive the ACK, so route not found!