Hi, same here, after upgrade to buster no X anymore. Normal start works, but ends at terminal login. Manual startx makes the screen flicker briefly, then back to terminal. X log contain no errors (EE).
Downgrade to stretch didn't change the situation in any way. Going back from linux 4.13 to 4.8 had no effect either. During downgrade gconf2 choked (triggers hung and never completed). During upgrade I think I saw some gconf error message too, but I cannot find a trace of them anywhere. Any advice would be highly appreciated. Thanks in advance Michael