Some additional information:

When the boot sequence is
- GRUB boot to recovery mode
- Drop to root prompt
- Remove a driver and install a driver
- Exit root prompt (Ctrl-D)
- Resume normal boot as per the recovery mode menu

Then the display comes up at a degraded resolution (1024x768) but no
gnome-session hang occurs in response to some of the reliable triggers
(typically, attempting to launch Firefox, Google Chrome, or navigate
gnome-settings).

Booting normally (via restart or hard-reset) brings up the display at
maximum resolution and gnome-session hangs immediately on one of the
reliable triggers.

I noted this previously.

To test whether resolution is the issue, I booted normally.  gnome-settings 
hangs gnome-session, so instead, I ran
```xrandr -s 1024x768```
which was immediately effective.  I then accessed gnome-settings and it 
triggered another gnome-session hang.

The conclusion is that degraded screen resolution itself does not
prevent gnome-session hangs.

Reviewing /var/log/syslog and the systemd journal, as well as
/var/log/Xorg.0.log reveals that gdm3 recognizes the monitor by
manufacturer and model and correctly picks up its configuration
capabilities when the system boots normally.  This does not occur,
however, when one boots first to recovery mode, changes drivers, and
resumes normal boot.

To test whether a recovery mode session alone prevented a gnome-session
hang, I then booted to recovery mode, did NOT change drivers, then
resumed normal boot.  Interestingly, the display came up in high
resolution notwithstanding the prior xrandr reconfiguration.
/var/log/Xorg.0.log reflected that gdm3 did identify the monitor.  And,
most importantly, the reliable triggers immediately caused a gnome-
session hang.

The conclusion, then, is that a recovery mode session alone does not
prevent a gnome-session hang.  One must change the driver during that
recovery mode session, to prevent it (albeit at the cost of degraded
screen resolution).

To test whether simply removing and installing the same driver during a
recovery mode session would be sufficient to avoid a gnome-session hang,
I experimented with that.  On resuming normal boot, the screen came up
at full resolution and the usual triggers produced a gnome-session hang.

The conclusion, then, is that a change of drivers is necessary during a
recovery mode session to prevent a gnome-session hang after resuming
normal boot from recovery mode.  Again, this is at the cost of degraded
screen resolution, and the protection will not persist through a normal
boot.

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https://bugs.launchpad.net/bugs/1892973

Title:
  gnome-session fails, and fails, and fails yet again

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