Some KDE widgets became broken after update


After an update, several KDE widgets stopped working with an error like this:
“file:///nix/store/xfiq9gl8gwr26bnq1bvdg5lvgqqacxwn-plasma-pa-5.27.8/share/plasma/plasmoids/org.kde.plasma.volume/contents/ui/main.qml:16:1: module “org.kde.plasma.private.volume” is not installed”

The list includes sound, networks, KDE connect, and possibly others. How do I fix this?
I tried nixos-rebuild switch --repair, but it didn’t find any broken packages. Deleting QML cache in $HOME didn’t help either.

The system is on the unstable channel.