Ubuntu – Gnome-system-monitor does not launch even after apt installation

18.04aptgnome

As instructed in other SO questions (Clicking on the system monitor button does not work anymore from one day to the next (Ubuntu 18.04) or System Monitor does not launch) I have installed the apt version of gnome-system-monitor, but I still get an error when my computer is using a lot of its memory and CPU. I am on Ubuntu 18.04.

~$ gnome-system-monitor 

(gnome system-monitor:6179): glibmm-CRITICAL **: 01:14:23.561: 
unhandled exception (type Glib::Error) in signal handler:
domain: g-io-error-quark
code  : 0
what  : Unable to find default local file monitor type

Further, I have also tried to follow advice on the launchpad to run echo 512 > /proc/sys/fs/inotify/max_user_instances to no avail

Any idea how to fix this? Thanks