I read the tutorial more carefully and by having the symptom that I described here it is almost like a timing issue with the driver loading…
There are several different cases where Lightdm can fail to start, mostly it is the case if the GPU driver is not loading at all or too late. what makes the X system fail to be available for lightdm.
If I could debug it that would be better, but I cannot take the cursor and the keyboard with CTRL+SHIFT in the debug window.