(close as many apps as possible to make the bug easier to reproduce)
1- Package the 1st Person template in Windowed Mode (edit GameUserSettings.ini)
2- Launch the game and press Windows key + D to bring the game in background
3- Press Windows key + D to bring the game back to foreground, see that the Space Key bar input is not received as the character does not jump. The released event is sill called.
Make sure the game is not the Active window when brought back to foreground, otherwise it's not possible to reproduce.
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-93711 in the post.