Input Actions bound to Any Key become unresponsive after mouse scroll until scrolled again

In UE latest release (5.5 launcher version), Enhanced Input Actions mapped to "Any Key" stop responding after scrolling the mouse wheel. Specifically, scrolling either up or down disables the Any Key input until the same scroll direction is performed again. For example, scrolling up disables the Any Key response until the user scrolls up again, at which point input detection resumes. This behavior consistently occurs with 100% repro rate and it occurs in UE 5.4 aswell.

The issue can be reproduced with a minimal setup: create an Enhanced Input Action, map it to Any Key, and observe that pressing any key triggers it. Then scroll the mouse wheel up or down and try pressing a key, no input will be registered until you scroll again in the same direction as before. A minimal repro project demonstrating this behavior is attached to this report.

Based on investigation of the engine source, MouseScrollUp and MouseScrollDown are treated as 1D axis input and not as discrete button presses. This behavior is handled in FEnhancedInputEditorProcessor::HandleMouseWheelOrGestureEvent. Because Any Key internally caches the first key pressed as CurrentlyInUseAnyKeySubstitute and waits for a release from that same key, and scroll input does not emit a release event, the system ends up in a state where input is blocked. Epic's internal feedback confirms this is a bug due to the lack of a release event from scroll input.

The licensee initially reported this issue, noting that it occurs in both editor and packaged builds. The licensee also emphasized that this is a critical blocker for console certification, as “Press Any Key” functionality must remain responsive at startup.

1. Create a new Input Action using the Enhanced Input system.
2. Map this Input Action to Any Key in your Input Mapping Context.
3. In a Player Controller or Pawn, bind the Input Action to respond to Triggered event (e.g., print a message when activated).
4. Run the project (in PIE or a packaged build).
5. Press any key, the Input Action should trigger as expected.
6. Scroll the mouse wheel up or down.
7. Press any key again, the Input Action no longer triggers.
8. Scroll the mouse wheel again in the same direction as before (up or down).
9. Press any key, the Input Action now triggers again.

This reproduces the issue 100% of the time in UE 5.4 and 5.5 launcher builds.