Unicast delay among few XBees

I have a little trouble using XBees.
For one coordinator and one router, it’s able to send and receive packet in and frequency. For one coordinator (A) and some routers (B and others, all XBees are in the same panID), if I put B far from others XBee alone, the unicast from A to B does work. However, if I put B among other XBees, the unicast packet delays about 1 second. This situation only occurs in few routers.

I don’t know why the delay happens in this situation. Please help me.

Thank you.

i think the problem with range of the ur network. however the router is useful only extended the range. suppose if you’re using coordinator as A and end device as B is far from the A the packet delivery is get delay or data mismatch will occur to avoid that thing in between we need keep router. if router it self is out of range we need to keep one more router in between them.

change antenna and check once more

Thanks for the answer, but I don’t think it’s about distance.
It happened even in only 50 cm from the coordinator and the router.

Thank you for the answer again!