Long touch on the line and you will get the‘What’s Here’ pop-up. (This applies to anywhere on the chart BTW)
On there will be text related to any relevant airspace or NOTAM. There is one titled ‘Exercises scheduled 4000’-8000’’. Touch that and all is explained. This will also paint a yellow line around the affected areas on the chart.
If you place a quick route in the area, you’ll also see this NOTAM in the NOTAM tab.