You can get a repro pretty easily with only BP by debug printing something on an enhanced input action press / release event, and also on debug press / release (e.g. in level script), holding down the key, then unfocusing the window by pressing the Windows key or something, which will call FlushPressedKeys - you'll see the debug release event fires, but the enhanced input event doesn't fire.
Result: The enhanced input action does not trigger, but the debug print strings will both print
Expected: The Enhanced Input action triggers when you press the windows key, even whilst holding down P. When you refocus the window (click into it or alt tab in) you can resume using inputs as normal.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-165730 in the post.