No RX on UART

Question

Hi, 
 I'm using 51822 to control GSM module via UART (57600, no flow control).
My device is USB and battery powered.
After I program the chip I HAVE to disconnect all the power in order to start system clean and have it working.
If I don't completely remove power on start nrf will send commands to GSM module, GSM module will recognize them and send a reply to nrf, but nrf won't get anything on RX (I'm using simple UART without interrupt and without softdevice). 
 What could it be? I also don't use 32khz xtal, so it synthesises clock from hf crystal.

Susheel Nuguru · Accepted Answer

uint32_t error;
 if(NRF_UART->EVENTS_ERROR !=0)
 {
 NRF_UART->EVENTS_ERROR = 0;
 error = NRF_UART->ERRORSRC;
 NRF_UART->ERRORSRC = error;

// flush the RX FIFO by reading and ignoring them

 

 while (NRF_UART->EVENTS_RXDRDY != 0) 
 { 
 error = NRF_UART->RXD; 
 NRF_UART->EVENTS_RXDRDY = 0;
 //Give a moment for more data in FIFO to move into RXD register
 nrf_delay_ms(1);
 }
 }