CCS/CC2650: Cannot run 2 tasks at once

Part Number: CC2650

Tool/software: Code Composer Studio

Starting from ProjectZero, I'm left only with advertising code which works perfectly. On this project I added another task that is receiving data from I2C, this code works fine in a standalone app. Creating the I2C task with a higher priority than advertising task will receive data to I2C as intended but it won't advertise. Same for advertising task, creating it with higher priority will advertise but won't receive data to I2C . 

If I add some breakpoints in code, case when advertising task has higher priority, it reaches all the breakpoints from advertising task and enters in I2C task and gets stuck at return of this function:

I2CSlaveDataGet(uint32_t ui32Base)
{
    //
    // Check the arguments.
    //
    ASSERT(I2CBaseValid(ui32Base));

    //
    // Read a byte.
    //
    return(HWREG(I2C0_BASE + I2C_O_SDR));
}

 So my conclusion is that the 2 tasks cannot run in the same time. maybe I'm missing something.

Thank you!