xbee communication lost

Dear colleagues,
I have simple instalation with Leonardo and Pro mini communicating over xbee network. There is a synchronious transmission of three bytes from Leonardo to Pro mini. If I send those three bytes every 4000 cycles it works great. If I try to send more often communication is lost. Leonardo is probably sending something what I can see on LED's on the shied, but most likely Pro mini is not able to receive those commands? I have changed boud rate between arduinos and xbees from 9600 to 38400 with no success. Any ideas?