Created a project in UE4 4.20.3 with an action mapping using the F key and Shift must be held down (Shift F). Print string for pressed and released. The string is printed on both events. Close project, open UE4 4.27 and select the 4.20.3 project and select convert in place. Try to press the key, the string is only printed for releasing the key and not pressing. Pressing no longer works. I was able to reproduce this bug and I can confirm you will get this bug all the time when upgrading the project from 4.20.3 to 4.27.
(the tag is animation because there aren’t any options relative to this topic and I had to put a tag in order to post)