Brush tool not working properly

I am having trouble with brushing on a layer mask to hide/reveal certain areas.  Specifically, I am trying to blend the edges of something I copied over from another photo.  However, the brush will not work correctly.  It seems to brush part of the area I want and then just stops doing anything, so I have these hard lines.  I do notice that when I choose a brush, the sample brush stroke is splotchy no matter which brush I choose, whether hard or feathered.  I am not using the Impressionist brush and my mode is set to normal.

Can someone help me figure out what is going on?

I have Photoshop Elements 2020 on a Windows 10  pc.

Thanks