Session hangs completely for several minutes with "no app for changed" messages

[Paul]

Once in a while the Gnome session wedges completely: no screen refresh, no mouse movement, etc. The system is still running and can be SSHed into. top via an SSH session shows no undue CPU load at this time, and no memory pressure. syslog has gnome-software "no app for changed" messages for many modules.

I sigh, start remotely HUPing various applications ... and then the session returns as if nothing had happened. (Not sure if it would have done so without closing applications.)

We'd better fix this before April.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: gnome-software 3.26.1-0ubuntu2.17.10.1
ProcVersionSignature: Ubuntu 4.13.0-31.34-generic 4.13.13
Uname: Linux 4.13.0-31-generic x86_64
ApportVersion: 2.20.7-0ubuntu3.7
Architecture: amd64
CurrentDesktop: GNOME
Date: Wed Feb 7 09:19:36 2018
InstallationDate: Installed on 2016-12-02 (430 days ago)
InstallationMedia: Ubuntu-GNOME 16.10 "Yakkety Yak" - Release amd64 (20161012.1)
InstalledPlugins:
 gnome-software-plugin-flatpak 3.26.1-0ubuntu2.17.10.1
 gnome-software-plugin-limba N/A
 gnome-software-plugin-snap 3.26.1-0ubuntu2.17.10.1
SourcePackage: gnome-software
UpgradeStatus: Upgraded to artful on 2017-10-12 (117 days ago)