This was intended behavior for the segments where you play as Jeff and Poo solo, since I didn't want you to be able to access their inventory (ATM Card, Sound Stone, Bicycle etc) without them present. However, when you play with a custom party or use Chaos Mode to have it randomly shuffled, this might impede your progress if you need to access the items (i.e. using the Hawk Eye in Deep Darkness).
So I might fix this by setting flags to hide the items only during those segments, rather than only show them when they're present in the party, that way you always have access to them regardless of the party leader you choose.
This was intended behavior for the segments where you play as Jeff and Poo solo, since I didn't want you to be able to access their inventory (ATM Card, Sound Stone, Bicycle etc) without them present. However, when you play with a custom party or use Chaos Mode to have it randomly shuffled, this might impede your progress if you need to access the items (i.e. using the Hawk Eye in Deep Darkness).
So I might fix this by setting flags to hide the items only during those segments, rather than only show them when they're present in the party, that way you always have access to them regardless of the party leader you choose.