I had a system crash/freeze recently and ever since hard resetting my system, the window list which pops up when you click on a (grouped) entry for an application (for example, you have many browser windows open) is incorrectly calculated/placed.

It seems that the individual window entries in the popup list have become slightly higher (ie: vertically larger) than they used to be but that the vertical space allotted to the entire window list is still based upon the original (ie: more compact) settings. The net result is that the popup window list will only show about 14 windows in the list before the remaining windows disappear under the task bar and off the bottom screen edge.

Does anybody know how to reset this sizing/positioning back to it's original value?

I'm running KDE Neon based upon the Ubuntu 16.04 release with everything upgraded to the latest versions. Specifically:
KDE Frameworks 5.30.0
Qt 5.7.1 (built against 5.7.0)

Can you do a screenshot what you mean exactly?

Certainly. Please see the following screenshot, lower left quadrant.

http://imgur.com/a/eH1NH

I have clicked on the Google Chrome icon in the task bar and the popup window list displays only 14 windows ... but I have a total of 20 Google Chrome windows open. After the original install, the vertical space allotted to each window in the popup window list was smaller and it would display all windows. Now the vertical size of each entry in the popup window list has become slightly larger and anything after the 14th window falls under the task bar and off the bottom of the screen.

Appreciate any tips you might have.

You should be able to scroll though the list by mouse wheel or with drag click.

Maybe ?
- Bug 375937 - regression: task manager group menu no longer shows all windows : https://bugs.kde.org/show_bug.cgi?id=375937

Rog131 wrote:Maybe ?
- Bug 375937 - regression: task manager group menu no longer shows all windows : https://bugs.kde.org/show_bug.cgi?id=375937

Yes, looks like this is my problem as well. Thanks for pointing this out, I'll keep and eye on the issue ...