First of all Heikin Ashi in NT is not accurate. I use them myself, but I build my own bars to match the real Heikin Ashi principles. The Close in NT is handled as the actual closing price. The division by four (OHLC) isn’t used. So HA in NT is more a mix of regular candles and HA, as the open is not based on the HA Open and HA Close, but the average of the HA Open and the actual Close. That is why the bars also look not like actual HA bars, too big bodies, volatile, not smoothed as ‘real’ Heikin Ashi.
To your question: your bars are loaded on enabling with a lookback period. Otherwise make sure to check there is enough data before executing orders (CurrentBar > x).