You shouldn’t think of Filtered decks as a permanent place to store those cards. It’s a way to construct a specific study session that doesn’t follow the usual scheduling or grouping of cards. When you’re done with that study session, you should Empty it so those cards are available for studying in their home decks on their regular schedule.
There are exceptions to that, of course, where you might want a Filtered deck to persist longer, but rather than leaving cards in the deck, it is usually better to modify your search filter to address that.
Especially if you’re trying to overstudy/cram your cards, you want the algorithm to know you’re doing that, so it can account for it in your future scheduling.