Another compositing manager is already running

I have been testing gnome 45.rc. I have built it myself using my scripts.
I am having a problem starting gnome-shell and mutter.
The error I get is: Window manager error: Another compositing manager is already running on screen 0 on display “:0”.
I am starting gnome using X11 xinitrc . e.g. XDG_SESSION_TYPE=x11 dbus-launch gnome-session --session=gnome
I have tried to find out about the compositor that is already running, but I haven’t found a way to do it.
The error is displayed from mutter src/x11/meta-x11-display.c
This is the same procedure I use to start gnome-44 which works fine.
Any thoughts?

Update 1: I fiddled around a bit and got GNOME to start under Wayland.
Using command: XDG_CURRENT_DESKTOP=GNOME dbus-run-session – gnome-shell --display-server --wayland
So, some issue with Xorg/startx .