EK-TM4C1294XL: trouble with SPI-read - erratic behavior of the uC, signal on scope seems okay

Dear Team,

I'm running into difficulties writing an SPI-Driver for an Analog Devices ADE7913 ADC. Reading the value from the SSI-resource yields strange behavior that I can't explain, yet the scope shows the expected value being written on the MISO line. I'll first go through the SW-steps, describe the problem including some screenshots, and will then provide a minimal working example. Any help is very appreciated!

Here's what the code does:

1. Issue a write command to the ADC, specifying the register we want to write to: 0x70

2. Send the value we want written into the register: 0xFF (I have tried other values, as well. The behavior is identical.)

3. Issue a read command to the ADC, specifying the register we want to read from (the same as was written before): 0x74

4. Execute a dummy write in order for the CS and SPI-clock-signals to be on the line: 0x00

5. Execute a read-command on the Tiva and write the data inside the FIFO into a variable

6. Print the variable and the status of the read command to the console

7. Restart loop at 1

As you can see on the scope-screenshot, the ADC sends the correct value in response to the read-command - The MISO-line is clearly receiving 0xFF:

However, the Tiva only reads the value correctly during the pass 4 and pass 8 of the loop (255 == 0xFF), and subsequently doesn't anymore:

Here's the code:

#include <iostream>
extern "C"
{
#include <stdint.h>
#include <stdio.h>
#include "inc/hw_memmap.h"
#include "inc/hw_ssi.h"
#include "inc/hw_types.h"
#include "driverlib/gpio.h"
#include "driverlib/pin_map.h"
#include "driverlib/rom_map.h"
#include "driverlib/sysctl.h"
#include "driverlib/ssi.h"
}


//*****************************************************************************
//
// System clock rate in Hz.
//
//*****************************************************************************
uint32_t g_ui32SysClock;

//*****************************************************************************
//
// The error routine that is called if the driver library encounters an error.
//
//*****************************************************************************
#ifdef DEBUG
void
__error__(char *pcFilename, uint32_t ui32Line)
{
}
#endif


// global constants
constexpr uint32_t ssiBitsPerSecond = 250'000;
constexpr uint32_t ssiDataWidthInBits = 8; // must be between 4 and 16


// global variables
int SSIreadStatus = -1;
uint32_t data = 0xffffffff;


// functions
void spiInit(void)
{
    // Enable SSI-Peripherals
    SysCtlPeripheralEnable(SYSCTL_PERIPH_SSI1);

    // Enable GPIO-Ports
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOB);
    SysCtlPeripheralEnable(SYSCTL_PERIPH_GPIOE);

    // Configure GPIO Pin Mux for SSI1
    GPIOPinConfigure(GPIO_PB5_SSI1CLK);
    GPIOPinConfigure(GPIO_PB4_SSI1FSS);
    GPIOPinConfigure(GPIO_PE4_SSI1XDAT0);
    GPIOPinConfigure(GPIO_PE5_SSI1XDAT1);

    // Configure the GPIO settings for the SSI pins. This function also relays
    // control of these pins to the SSI hardware.
    GPIOPinTypeSSI(GPIO_PORTB_BASE, GPIO_PIN_4 | GPIO_PIN_5);
    GPIOPinTypeSSI(GPIO_PORTE_BASE, GPIO_PIN_4 | GPIO_PIN_5);

    // Configure and enable SSI1 port for SPI master mode
    SSIConfigSetExpClk(SSI1_BASE, g_ui32SysClock, SSI_FRF_MOTO_MODE_3,
                       SSI_MODE_MASTER, ssiBitsPerSecond, ssiDataWidthInBits);

    // Enable modules SSI0, SSI1, SSI3.
    SSIEnable(SSI1_BASE);
}



int main(void)
{
    // Run from the PLL at 120 MHz.
    // Note: SYSCTL_CFG_VCO_240 is a new setting provided in TivaWare 2.2.x and
    // later to better reflect the actual VCO speed due to SYSCTL#22.
     g_ui32SysClock = MAP_SysCtlClockFreqSet((SYSCTL_XTAL_25MHZ |
                                             SYSCTL_OSC_MAIN |
                                             SYSCTL_USE_PLL |
                                             SYSCTL_CFG_VCO_240), 120000000);
     printf("g_ui32SysClock = %d\n\n", g_ui32SysClock);

    spiInit();

    int count = 0;

    while(1)
    {

        // SPI-Test: Write to EMI_CTRL register of ADE7912. Then read written value from ADE7912.
        {
            SSIDataPut(SSI1_BASE, ((0xE << 3) | 0b000));
            SSIDataPut(SSI1_BASE, 0xFF);

            while(SSIBusy(SSI1_BASE))
            {
            }

            SSIDataPut(SSI1_BASE, ((0xE << 3) | 0b100));
//            HWREG(SSI1_BASE + SSI_O_DR) = ((0xE << 3) | 0b100); // write-command on register level (vs. TivaWare)
            SSIDataPut(SSI1_BASE, 0); // a secondary write is necessary for the SPI clk and CS~ to activate during reading. any value can be written.
//            HWREG(SSI1_BASE + SSI_O_DR) = ((0xE << 3) | 0b000);

            SSIreadStatus = SSIDataGetNonBlocking(SSI1_BASE, &data);
//            data = HWREG(SSI1_BASE + SSI_O_DR); // read-command on register level (vs. TivaWare)

            printf("Pass %d - EMI_CTRL register value: %d\n", count, data);
            printf("SSIreadStatus: %d\n\n", SSIreadStatus);

            ++count;
        }

        SysCtlDelay(g_ui32SysClock / 250 / 3);
    }
}

I'm a bit clueless at this point. Does anyone have an idea what I might be doing wrong?