Xbee ZB S2 - rx pin problem

i have a problem with xb24-zwit modules with 23A7 firmware.
I use a atmega328 rx tx connected to tx rx of xbee. After start-up, some times, the rx pin of xbee don’t work but the tx pin work fine. If i send AT command to radio, the radio don’t execute command (for example FR reset) but if the radio receive data from the coordinator, the tx pin work fine and send data to processor. Also the pin assoc work correctly reporting the status of association.
I tried to reset the processor but the radio still does not respond to commands. The radio receives correctly only after a hardware reset or restart supply.

Thanks for the support

Three questions. First, what voltgeate level is your ATMEGA328 running at?
Question 2, when you issue the command, are you issuing the Command mode sequence of 1 second of silence, +++ within 1 second, followed by 1 second of silence?
Question 3, Are you using a voltage divirder or level shifter between the two devices?

the ATMEGA328 is running at 5V. I issuing AT command in API mode with xbee-arduino library and yes, i using a voltage divider between the two devices.