Too much deliver_status ! = "00"

Dear
We have a model of router 1, 3 endpoints, one coordinator. We use, Arduino Uno for all, ans XBee S2c Pro:

  • All in API2 (FirmW#4055)
  • EndPoint, router and Coordinator have the same ST SP.
  • only EP are fixed SM5 (which defines them as EP)
  • the coordinator sends a packet to each EP one after another.
  • all are in an office, without obstacle, we have an acknowledgment of receipt, ie non delivred TX status (deliver_status! = "00") goshawks 30%, which seems to us enormous.

Why the failure rate?
Cordially.