I am using XBee XB24CZ7UIS modules with ZigBee 4043 firmware version for data transfer over SPI in API mode Without Escapes. I have ZigBee network with Coordinator (master) and only one End device (slave). Master sends packet to slave every 100ms and slave response him by single data packet. Everything works fine but after random time, master start reading only 0xFF bytes from SPI. Writing to SPI is OK because master is still sending new packets by AT Transmit request command. Receiving of incomming packets also works because RSSI PWM signal is changing according to distance of slave module. Only reading SPI from XBee module still returns 0xFF. Only way how to fix this state is to reset XBee module. After reset, module is working again for few minutes or seconds to next SPI fail. Can anyone help me to fix this problem? Thanks.