IWR6843: Conflict between multiple tasks & task priority in TI mmWave IWR devices

I'm not sure whether the same issue happens for other TI products such as MSP430 and AWR mmWave, but for IWR mmWave radar, I realize that I can't perform multiple tasks in a same block (sub-routine) simultaneously. For example, original source code of 3D_people_count and HVAC in toolbox 4.2.1 can do UART function normally (in subroutine InitTask). But after I added SPI_init and set-up SPI parameters in the same block, then in main() I do Task_create(InitTask), all function in InitTask can't not be executed, they can only be executed separately. Is it related to thread timing of TI RTOS? Please explain and tell me solution with sample code to run many function in a task.