UART2 Transmit Holding Register is always full

hi , dialog
We use SDK V1.06 pxp_reporter demo. After each end of the BLE advertisement , we used UART2 to printf string . At first , it can print the string normally. But we found it will stuck in " while (hw_uart_write_buf_full(uart)); " later. It seems that there is something wrong with uart after the system waking up from extended sleep mode. Our code is as follow :

静态孔隙periph_init(空白)
{
hw_gpio_set_pin_function(HW_GPIO_PORT_1, HW_GPIO_PIN_0, HW_GPIO_MODE_OUTPUT,
HW_GPIO_FUNC_UART2_TX);
hw_gpio_set_pin_function(HW_GPIO_PORT_1, HW_GPIO_PIN_2, HW_GPIO_MODE_INPUT,
HW_GPIO_FUNC_UART2_RX);
}

void retarget_init(void)
{
uart_config uart_init = {
.baud_rate = HW_UART_BAUDRATE_115200,
.data = HW_UART_DATABITS_8,
.stop = HW_UART_STOPBITS_1,
.parity = HW_UART_PARITY_NONE,
.use_dma = 0,
.use_fifo = 1,
.rx_dma_channel = HW_DMA_CHANNEL_INVALID,
.tx_dma_channel = HW_DMA_CHANNEL_2,
};

hw_uart_init(HW_UART2, &uart_init);
}

{
...
hw_uart_send（HW_UART2 , “\r\n123412341234\r\n”）;
...
}

void hw_uart_write(HW_UART_ID uart, uint8_t data)
{
// Wait if Transmit Holding Register is full
while (hw_uart_write_buf_full(uart)); // stuck here

// Write data to the transmit FIFO
UBA(uart)->UART2_RBR_THR_DLL_REG = data;
}

Is something wrong with my code?