I have observed this issue which is very similar to UE-62458 and other questions that have been posted here. As an additional detail, however, I found that inserting a Delay node produces the desired results. This indicates that the variables are in fact being set, just in the wrong order.
Following the steps listed here: Unreal Engine Issues and Bug Tracker (UE-62458)
- In Event BeginPlay, before the Print String node, add a Delay node with a value of 0.0 (this delays until the next frame).
- Press Play
Results: The value of the input node will be printed.