The bug https://bugs.kde.org/show_bug.cgi?id=359634 has reappeared in 4:5.5.4+git20160225.0001+15.10-0 , just that now all the widgets are missing. Probably the package usually providing these QMLs has not been installed in the last upgrade.
The problem can be solved by following steps described at: http://jriddell.org/2016/02/23/kde-neon-comes-alive/