If you change focus to the Blueprint Editor (Alt+tab) while a Microsoft IME keyboard is active, the editor will freeze for a short time. The duration of the freeze is dependent on the number of blueprints open and their complexity.
Note: This is specific to Windows 8 and 10. It does not occur in Windows 7. This also only occurs with the Blueprint Editor.
This also occurred in 4.14
Head over to the existing AnswerHub thread and let us know what's up.