This got partially fixed within Plasma 5.6
Breeze GTK
Gtk3: Fix wrong filename of scrollbar. Commit. (Code review # 127323. Code review # 126970. Fixes bug #356395) Do not install development helper files via cmake. Commit.
see: https://www.kde.org/announcements/plasma-5.5.5-5.6.0-changelog.php
This got partially fixed within Plasma 5.6
Breeze GTK
Gtk3: Fix wrong filename of scrollbar. Commit. (Code review # 127323. Code review # 126970. Fixes bug #356395)
Do not install development helper files via cmake. Commit.
see: https:/ /www.kde. org/announcemen ts/plasma- 5.5.5-5. 6.0-changelog. php