Xbee pro S39 more than 20+

so i have 20+ Devices BeagleBone with Xbee pro S39 with main command computer the problem is on start i have to send a hand shake signal from the MC unit for all other devices and every time i only get a reply from only 8 devices

Sounds like you need to add some more delay in the response from the network as they are all trying to respond at the same time.

i can’t add any delay in the response

Then you may need to switch to a Polled system instead.