KNotifications uses sound which you set in your .notifyrc file. To prevent overlapping files the name of the files were renamed when moving from kde-runtime to plasma-desktop.
You will nedd to update your .notifyrc file for this, e.g. Sound=KDE-Sys-Log-Out.ogg is now Sound=Oxygen-Sys-Log-Out.ogg I've added this to https://community.kde.org/Frameworks/Porting_Notes#KNotifications_Changes Jonathan
