Hi, There is an issue when using an old AppStream version (older than 0.12) with plasma-desktop. It would sometimes crash. Since it's an optional feature and not central to plasma's usability overall, we decided to just bump the version, understanding that lacking the feature is better than crashing.
We recommend to upgrade AppStream to the newer stable release (with this fix and others) or to just build plasma-desktop without the AppStream integration if the version of the library is simply too old. Sorry for the inconvenience. Aleix https://bugs.kde.org/show_bug.cgi?id=391468 https://phabricator.kde.org/D15263