Hi, Adams answer isn’t strictly true …
construction scripts also run when you compile and save a blueprint, even if you haven’t changed anything in the BP 
(technically it may be destroying and recreating the nodes?) … anyway…
In my case I have nodes that are all of the same class (BP) that need to know which other nodes of the same class they overlap with in the Editor. The obvious problem is that the first one I place in the scene overlaps with no others as there is nothing to overlap with. If I place the second one in the scene, overlapping with the first, its construction script spots the overlap … but the first node will need to rerun its construction script again to spot the overlap. So the simple answer for me is place all the nodes in the scene that I want and then compile and save the BP.
Hope this helps, I realise that it’s not automatic but for my use case it’s perfect.
rOb