Since the Krusader 2.7.0 release, the paragraph:
Krusader uses icons which are only contained in KDE's default icon set Breeze. Make sure you have it installed and that it is used by KDE applications. Unfortunately you cannot use a different icon set because it will most likely not contain all icons needed in contrast to the very large set in Breeze.
of https://krusader.org/report-bugs/index.html could be substituted by an updated text like
Krusader uses icons which are contained in KDE Plasma's default icon set Breeze or other icon sets like Oxygen, make sure you have at least one of them installed. Other icon sets will most likely not contain all icons needed.
as it can be seen in https://krusader.org/release/2.7.0/release_notes.txt and https://docs.kde.org/trunk5/en/extragear-utils/krusader/konfigurator.html
Suggestions are welcome :-)