NinjaTrader has marked today's date as Holiday, that is the reason NinjaTrader is unable to pull today's data.
Please follow the below steps:
This would work for both NinjaTrader 7 & 8:
Step 1 >> Right click on the Chart..
Step 2 >> And then go into Data Series..
Step 3 >> Then under Trading hours you can select >> Default 24/7
Now you will see that the chart is loading fine.