Quick answer: Unity Input System with Update Mode = Fixed missing inputs between physics ticks? Fixed mode polls on fixed timestep; events between are lost - use Update mode for action games.
Player presses key between physics ticks; input dropped; action doesn't fire.
Use Update mode
InputSystem.settings.updateMode = ProcessEventsInDynamicUpdate. Polls per frame.
Or buffer inputs
Capture inputs every frame; consume on physics tick. No drops.
Audit per game type
FPS / arcade: Update. Strategy / turn-based: Fixed. Document the choice.
“Input timing depends on update mode. Match to game type.”
If your game has missed inputs, the update mode is the first suspect. Audit; switch if needed.