It's possibly caused by some KDE frameworks packages being stuck in 5.22 and not migrating from unstable to testing (while others already being 5.23). I was lax and allowed this mix this time, and again it shows that it should never be done until all of the frameworks packages are the same version (same applies to Plasma packages I suppose).
Example of stuck packages (looks like they fail to build on some archs): https://tracker.debian.org/pkg/baloo-kf5 https://tracker.debian.org/pkg/ki18n Regards, Hillel Lubman.
