Why wont my flatten tool work when dragging the mouse across my terrain?

I have a student that was using the terrain flattening tool as normal, he set the path of the height he wanted then should be able to drag and lower any highlighted sections to the same level as he started with, but it isn’t working. I had checked all his settings for his tool and it doesn’t look like hes changed any big settings.

Has anyone else had this problem before, and have a solution?

I’m attaching a pic of his screen

Note In the pic he have Landscape 2 selected in the Landscape Editor but when we changed it to Landscape1 it still didn’t work.

So we found out right after I posted the question.

Apparently he had the Sequencer open in another window and because of that being open it somehow bugged the landscape editing tool to not work. It looks like you can only have one viewport open when using the Landscape Flattening tool or you will have this bug.