I have this issue frequently. A few things i have noticed causing a problems.
Setting xbee.idle_radio(True) will not allow other units to send messages to that device, or find it with node discover. ALSO, that particular xbee will not find anyone else with its node discover, xbee.discover()
Setting xbee.idle_radio(False) brings it back inline when that is the issue.
The other problem i find gets me in a no-rf traffic state seems to be related to the CCA mechanism. The CA values for Xbee3 are less tolerant to noise and it seems like if it "fails" (increments up the CCA failures in EC) too many times it is left in a dead state. I have no figured out how to recover without a reboot. Setting CA=0 (disable) has seemed to be helpful in stopping it from happening, but it might just take longer to get there. You have to set CA=0, store it with WR and reboot.
When in this state, even trying to send BROADCAST messages were saying "ETIMEDOUT" and the EC value would go up by 3, no data would be sent out the RF