WidgetBlueprintLibrary::DrawLines which calls FSlateDrawElement::MakeLines has broken AA for sharp cornered lines.
Draw an anti-aliased line with a sharp change in direction using WidgetBlueprint::DrawLines. Here's one way to rig it:
New Widget Blueprint
Override OnPaint event as follows:
OnPaint -> Draw Lines -> return
Where Draw Lines takes an array of
200,100; 300,500; 320,100
Add new widget to level UI graph
Event BeginPlay -> Create widget -> Add to viewport
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-30481 in the post.