Just yesterday I installed PPro CC2020 on a secondary computer (my primary computer has other issues so I had to improvise). I proceeded to edit a video today, and I needed to replace a piece of the frame where a Powerpoint slide shown on a TV had been slow to advance. So I took a frame capture of a frame that showed the correct slide, placed it on an upper track, and added a 4-point mask to its Opacity effect. It defaulted to 10px feather and a small rectangle in the center of the frame, which I guess is normal. Then I then dragged each corner of the mask (blue line) to the edges of the TV and reduced the feather, but the resulting mask did not change! The screenshot below tells the story. The portion of the image that is actually opaque is not where the blue lines are, but the original feathered rectangle in the center of the frame - just the top right portion of the desired slide (more pinkish tan art) and less of the speaker's shoulder because he had shifted his weight.
I tried removing the rectangle mask and making a freeform bezier mask instead, but once I completed the shape, the opacity once again became that first rectangle from the 4-point mask! If I turn the Opacity off or remove any/all masks, the full frame reappears as it should. But I can't get the shape of any mask to be anything other than that original small feathered rectangle.
As a workaround, instead of using a mask in PPro I edited the image in Photoshop to make everything but the TV transparent, but that shouldn't be necessary. Has anyone else seen this behavior?