No window manager used at startup!

Since mars 30th, every time my system start, I have no window manager used! I can set the window manager Marco or Compiz by navigate to control center>mate tweak>set a window manager>OK. But after each restart, same problem: no window manager used. If I set Compiz then I restart, same problem. If I set Marco then I restart, same problem. With no window manager used, I can't use my computer! I can't close the windows or switch the windows. I don't understand why. In normal condition, the following command returned:

wmctrl -m
    Name: Metacity (Marco)
    Class: N/A
    PID: N/A
    Window manager's "showing the desktop" mode: OFF

But currently, at startup, as no window manager is used, this command returned (see capture bellow).

Please help, how to fix it?

The only thing I did with terminal since my problem is the following commands, to set a specific GTK to LibreOffice. Is there a link to my problem with no window manager used at startup ?

find /usr/share/applications -name libreoffice* | xargs -i cp {} ~/.local/share/applications
find ~/.local/share/applications -name libreoffice* | xargs sed -i "s/Exec=/Exec=env GTK_THEME=$GTK_THEME /g"

tried adding marco --replace or compiz --replace to your startup items? that works for me

I want to do this temporarily, but I want to fix it. What is the procedure to identify the root cause?

Possibly (not sure at all) window manager need to restore to default. Shutdown or reboot don't do this.
Carefully, this trick restarts, but will close all your running apps. Close all, before procedure:
sudo service lightdm restart

Restart lightdm didn't fix. I give up, I let compiz --replace in the Startup Apps.