Spline point manipulation does not work properly when the spline component is selected. Although the widget appears on a spline point, applying a translation results in the entire spline component being translated rather than just the point. Also after translation, the current point selection is cleared in the details panel.
At some point it seemed like it was possible to subsequently select a point in the Level Editor viewport and continue working. But now just selecting the spline component makes it impossible to edit spline points.
This is a significant workflow issue making it difficult for artists to iterate on splines since it makes it impossible to simultaneously edit spline points in the details panel and manipulate them in the viewport. It is only possible to edit spline points in the viewport when the actor is selected now.
Entire spline moves and the spline point selection is reset (widget is no longer at spline point and details panel does not show the selected spline point's properties).
Spline point moves and the spline point remains selected (widget is still at spline point and details panel still shows the selected spline point's properties).
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-153875 in the post.