I can see you've already got some, so I believe one of the following is happening, 1 - Only the first three runs each week can drop a mod, the three for which the chalice gives 'bonus rewards' / used to give 'powerful rewards'. 2 - There's no 'knock-out' system to remove duplicates from the pool, even though they are unlockables and not consumables. So it could well have tried to give you one you've already got, and in that case the attempt is used up and you don't get any kind of notification.