This looks like bug 982889, but that was fixed in 2013.
Still, since this is the only remaining instance of this bug I have
heard of I would recommend upgrading to Ubuntu 18.04. It is also a long
term support release and if you find gnome-shell is not well suited to
this machine then you can
This seems to be a recurring error in your logs:
[26.747] (EE)
Fatal server error:
[26.747] (EE) Cannot run in framebuffer mode. Please specify busIDs
for all framebuffer devices
That's probably the issue.
** Package changed: xorg (Ubuntu) => xorg-server (Ubuntu)
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You
