Part Number: TM4C1294NCPDT
Tool/software: TI-RTOS
regarding this question:

I have found out that the answer is the newly added required calls:
USBDCDFeatureSet(0, USBLIB_FEATURE_CPUCLK, &ui32SysClock);
USBDCDFeatureSet(0, USBLIB_FEATURE_USBPLL, &ui32PLLRate);