A wall has splited into several piece

I’m drawing a house in sketchup, and what a surprise when a wall have been splited into several pieces without any line.
Look at the photo I’ve joined. I have colored intentionally to see the different fragments.
Where the problem come from ? And how can I correct it ?
Thank you

you’ve moved a line somewhere and it distorted your wall.
Under View, you can turn on hidden geometry to see the new lines.

Thank you.
I’ve done what you said and now I can see the hidden lines.
I just have to delete them ? And it will return to normal ?

no, if you delete them, the wall face will just disappear. Your wall is no longer ‘flat’ (on the same plane). You will have to solve that problem to fix this issue

Generally it’s faster and easier to erase the problem geometry and redraw than to attempt repairs.
Turn off hidden geometry before you begin erasing.
That way, the hidden lines will simply disappear along with the face.

I had done that but when I redraw the wall, the same problem come back. So, with the function Hidden geometry, I had deleted all the bad lines and my wall is normal again.