From my testing, it appears that Shift+F is not detected by the editor. If you map the input action to either F or Ctrl+F, they both work correctly, so it seems specific to the Shift+F keyboard combination.
Tested in //UE4/Release-4.26 @ CL 15973114 and this did not occur, so marking as a Regression
Shift V prints out it's text correctly, but nothing happens for Shift F
Both Shift V and Shift F would print out their values when pressed
There's no existing public thread on this issue, so head over to AnswerHub just mention UE-122053 in the post.