That file is not there in Ubuntu Mate, but it is there is Manjaro Mate. Hmm.
Meanwhile, in /.local/shared, I found xorg.0.log which seems to be filled mostly with graphics card information.
I think I may have found some clues, but it is too late to work on it now. In brief, I think those files that the log says cannot be found are in a different location. I can try working on it tomorrow.