Thanks, do you mean if you're using 2 different binds for the same side? If so then yes, it seems godot's input handler doesn't activate the is_action_just_pressed() function if you're already holding another button linked to that action. I'll try to see if I can find a workaround to make that work.
If you are just using 1 button for each input, then hmm I haven't seen that before, I'll look into it more. To clarify, do you mean that if you press both, keep holding left, then you can't press right (or vice versa)? Does it seem to matter if a note is there (left, right, both or neither)?
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Heya! Sorry for replying so late. What I was referring to seemed to be a keyboard issue -- I just used the normal singular bindings, and the issue's stopped now that I'm using a new keyboard. For context, though, the issue was that sometimes tapping *both* keys simultaneously caused one of them to not be registered. When this happened, letting go of the key that didn't register would register a "tap" at that moment. Even though I only noticed it in this game, it seems like it was a hardware issue instead of a game issue.
In another note, I would totally support the addition of more control schemes! When I play this game, I use DF JK, with the keys being bound as ZX ZX.