Subdivide don't work on some faces (only split edges). Why?

On a scene i have a regular plane that i need to subdivide to modify it with a shape key (to make it “collapse”).
But only some faces are subdividing, the others are creating vertex only on the edges, when i need new vertex inside the face.
Video illustrating this :

Do someone know why it happens and how to solve this?

The problem is that the faces you are having problems subdividing are not quads. They are ngons. They have more than 4 vertices and more than 4 edges.

When you selectively subdivide single faces one at a time you are creating ngons of all quads that shared edges with the original face. The solution is to subdivide all the faces at the same time.

From the Blender manual.

A workaround would be to select the appropriate vertices on the ngon and hit J to join them.

1 Like