Mesh invisible to the player?

Hello, I would like to know why this part of the mesh is invisible when I press P or use standalone player like in the pictures below. I don’t get it. The face is there as all the others, but is invisible when I run the game.

this is the mesh ^
and this is when I press P to play:

flipped normals?

Never thought that could be indeed that. Thank you. Solved.