Mesh not bending smoothly to bones As you can see the in the screenshot below the mesh is not bending smoothly according to the pose of the bones.

There are more than enough subdivisions. But the weight paint is irregular.

Link to blend file.
https://drive.google.com/open?id=1ZNfettFy4mPaNWBkJT7hq_6CnJ4qBzoI
It seems to be a subdivision issue.
I cleared the parent, subdivided the plane and parented it again with automatic weights. It works fine then I think.

Edit: Here is the edited file: https://drive.google.com/open?id=1kZZFuC196PkZ_omzLCpyDzy4sQYdYoy3