Comment 1 for bug 1826271

Hi Michael,
none of the updates we have made to virt-manager since Bionic released seems related to the issue you are describing.

Furthermore I just checked this on my 18.04 and it is saving the preferences just fine (default Desktop, not KDE).

This is stored in config option "/stats/enable-disk-poll"
I think this uses gconf, so maybe something is (now) missing in your KDE environment?
All is stored under "org.virt-manager.virt-manager" namespace.

[1]: tells us that this is dconf based.
 $ dconf-editor
And I find org.virt-manager.virt-manager/stats/enable-disk-poll in there with my value (I enabled it).
It even shows that it is modified from the default (off) and lets me change it.

This should be stored in permanently in:
  /home/<user>/.config/dconf/user
and some live only data
  /run/user/1000/dconf/user

Questions:
- Do you have these files
- how do the virt-manager values appear with dconf-editor for you?
- can you persists the values with dconf-editor?

[1]: https://askubuntu.com/questions/249887/gconf-dconf-gsettings-and-the-relationship-between-them
[2]: https://askubuntu.com/questions/15262/graphical-editor-for-gsettings-dconf