Emerging kde-plasma/systemsettings-5.11.1 misses to pull kde-frameworks/kactivities-stats dependency. Attached the build.log of the failure. Emerging kactivities-stats solves the issue.
The Attachment is missing. Please reopen.
Sorry, but bugzilla kept giving me ERR_ACCESS_DENIED when uploading the file. Anyway, if you like at systemsettings sources, and in particular https://github.com/KDE/systemsettings/blob/master/CMakeLists.txt you'll notice the ActivitiesStats requirement, so the build.log is not informative. This is a simple missing dependency in the ebuild.
Created attachment 499140 [details] build.log
But that's master branch. Anyway, the same commit introducing the depencency is also found in Plasma/5.11 branch, so this is confirmed.
Thanks, fixed in git commit 3560ca081d5a8b2499413364db01b295393d07ad