Hello,
While organizing my BP code by splitting into multiple Event Graphs, I’ve noticed that various nodes and links disappear during copy/cut and paste process. It is a nightmare for huge BP graphs!
You can reproduce issue;
Step 1: Create a “Reflections” project from UE4 sample projects library.
Step 2: Open Level BP. Select bottom comment box (including all components within). Cut.
Step 3: Add a new Event Graph.
Step 4: Switch to new Event Graph, and Paste 
It gets worse with huge BP codes; a majority of custom events, timelines, variables and links disappear!