It broke before but could be fixed by enabling the nepomuk USE-flag for kdelibs. But now it is gone and so is the information in the dialogue. See also:
Is this working for anyone in Gentoo?
It is a regression caused by nepomuk removal. To fix it, we would have to restore at least soprano.
Fixed in KDE Frameworks 5.20
(In reply to Andreas Sturmlechner from comment #2)
> Fixed in KDE Frameworks 5.20
KDE Plasma 5.5.5 is stable now and KDE Frameworks 5.20.0 is available in tree.