I was doing slayer and they gave me two clue scroll (hard) at the same time it is reported as an error or it is normal that two are output at the same time
You are only able to have in your possession one clue scroll of each tier at a time, either in your inventory or bank. Whilst multiple clue scrolls of the same tier can be dropped (which often happens with quick successive kills, ie. when using a multicannon), you will only be able to pick up one. Once you pick up the clue scroll, you will not see another clue of that tier drop again until you either drop the scroll, or complete it.