Starting idle task using Task Manager library frequently throws error "Unknown function at 0x000008C8" when running with the debugger (often takes several restarts until it runs).

Question

Starting idle task using Task Manager library frequently throws error "Unknown function at 0x000008C8" when running with the debugger (often takes several restarts until it runs). I am using SDK14.2.0 and SES 3.34.

The failure occurs at line 263 in task_manager.c where a jump to the idle task is performed:
idle_task(p_idle_task_context);

In my project I am using CLI library with task manager and I also have timers running which post events to the scheduler that then calls a specific handler for the timer event. My idle loop looks like this:

void idle_task(void * p_context)
{
    for (;;)
    {
        app_sched_execute();
        NRF_LOG_PROCESS();
        task_yield();
    }
}

The timers that post to the scheduler do not seem to be the issue. If I don't start any of them I still see this issue quite often.

My main startup code looks like this:

int main(void)
{
    ret_code_t err_code = NRF_SUCCESS;

    // logging and cli init
    err_code = NRF_LOG_INIT(systick_getTickCount);
    APP_ERROR_CHECK(err_code);

    nrf_drv_uart_config_t uart_config = NRF_DRV_UART_DEFAULT_CONFIG;
    uart_config.pseltxd = 4;
    uart_config.pselrxd = 30;
    uart_config.hwfc    = NRF_UART_HWFC_DISABLED;
    err_code = nrf_cli_init(&m_cli_uart, &uart_config, true, true, NRF_LOG_SEVERITY_INFO);
    APP_ERROR_CHECK(err_code);

    // init clocks
    err_code = nrf_drv_clock_init();
    APP_ERROR_CHECK(err_code);
    nrf_drv_clock_lfclk_request(NULL);

    systick_init();

    APP_SCHED_INIT(SCHEDULER_MAX_EVENT_SIZE, SCHEDULER_QUEUE_SIZE);
    // App timer uses the scheduler (APP_TIMER_CONFIG_USE_SCHEDULER=1 in sdk_config.h)
    err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);

    APP_ERROR_CHECK(nrf_cli_task_create(&m_cli_uart));

    // initialize BLE stack and services
    ble_stack_init();
    ble_peripheral_init();

    // Start execution
    NRF_LOG_INFO("===== Application Started =====");

    task_manager_start(idle_task, NULL);
}

Any help would be greatly appreciated. I have an approaching deadline and have spent alot of time trying to see what could be going wrong. I don't "think" this issue occurs with Release build but I have not tried enough to be sure, but nonetheless this shouldn't happen when running the debugger.