Gnome-shell consuming memory

[Colin Law]

On one of my machines which has been upgraded over several years and
is now running 19.10 just one of the configured users appears to be
seeing a dramatic memory leak in gnome-shell, even when nothing is
happening on the UI. Immediately after logging on, using the Ubuntu
selection from the logon screen, gnome shell shows as using about
134MB. From there it climbs at about 300MB per hour and after a few
hours the machine grinds to a crawl, not surprisingly. This happens
even if the user logs on and then the machine is left completely
alone. Logout and back in frees all the memory.
A test user I have configured sees no such problem.
I have uninstalled all extensions apart from the system ones, disabled
all the system ones and reset all the gnome settings using dconf reset
-f /org/gnome/ to no avail. Also I have removed
~/.local/share/gnome-shell and allowed it to recreate it.
Also I have removed .compiz, .config/dconf/user, .gconf, .gnome, .gnome2.
I can't see anything obvious in the log.
It must be something in my settings that is triggering it as the other
user does not see it, but I have run out of ideas on what to try.
All suggestions (within reason) gratefully received.
Switching away from gnome is not considered to be within reason :)

Colin Law