SUMMARY
As the title reads, some icons throughout Plasma tend to be rendered blurry or missing entirely. This tends to happen when an application is installed/removed/updated or if the icon theme changes. Applying new accent colors via the wallpaper sometimes trigger this too (this is also considered a 'theme change'). The only way to rectify the problem is to manually restart plasmashell with "kquitapp5 plasmashell && kstart5 plasmashell > /dev/null 2>&1 || kstart5 plasmashell > /dev/null 2>&1", afterwards all icons show normally...until another application gets updated. I am using the Breeze Dark and "Redmond Dark with Square Highlights" by Paul Mc Auley, which inherits the Breeze Dark icons anyway. It is also reproducible with any other icon-theme I've tried.


STEPS TO REPRODUCE
1. Start Plasma.
2. Change the icon theme in System Settings.
3. Open the Application Launcher (Kickoff) and find entries with missing icons scattered around.

OBSERVED RESULT
As the title reads, some icons throughout Plasma tend to be rendered blurry or missing entirely.

EXPECTED RESULT
All application icons show normally in Plasma's widgets and application menu (that's a widget...)

SOFTWARE/OS VERSIONS
Operating System: openSUSE Leap 15.4
KDE Plasma Version: 5.25.4
KDE Frameworks Version: 5.96.0
Qt Version: 5.15.5
Kernel Version: 5.14.21-150400.24.11-default (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-3320M CPU @ 2.60GHz
Memory: 7.6 GiB of RAM
Graphics Processor: Mesa DRI Intel® HD Graphics 4000


ADDITIONAL INFORMATION
Oddly enough, when the bug occurs, the same icons go missing almost every-time: Heimdall, AntiMicro, SpeedCrunch, RetroArch, XTerm, Zotero. These icons get blurry every-time when shown in categories in the Kicker (smaller icons): System Settings, Dolphin. The 'Battery and Brightness' widget has blurry icons in its notifications too.