Tried pasting an existing state machine node into a new state machine’s graph (because, science!) and the UE4 editor instantly crashed. Reproduced easily in a new template project as well.
"We apologize for the inconvenience.
Please send this crash report to help improve our software.
Thank You for the report. We are aware of this issue and are currently working on it. I am going to condense this post into one by Duncan Dam as you are both reporting the same issue. I want to be able to answer you both as quickly as possible.