1D chart has only one value of the MA per day, therefore only this value is known on any intraday resolution.
The value of the MA can be seen on the last intraday bar of daily session (confirmed value), and other intraday bars display N/A simply because there's no confirmed daily MA value on it.
For example, if a symbol is traded 24 hours a day, the 15-min chart will have 96 bars per trading session, therefore, the value of the 1D resolution will be displayed on each 96th bar – at the last bar of the day. In this case, the time of the last bar of the session is 23:45 – at this time you'll see the daily MA value, while other bars will show N/A.
If the chart is zoomed in, the indicator is displayed as a straight line, but if you zoom it out you'll see that it's plotted correctly.