Filtered Deck Problem

I have marked all my cards (more than 5000 pieces) with a keyword. Now I want to create a selection stack from all cards with this keyword. I limit the selection stack to 5000 cards. Why are only a small number of cards added to this selection pile, although all 5000 cards are marked accordingly?

“For efficiency reasons, if your cram deck contains more than 1000 cards, only 1000 cards will be shown as due on the deck list and study screens.”

The limit has been increased since that was written. I suspect in this case the filtered deck search terms are either too specific, or cards have been excluded because they’re in a different filtered deck, suspended, etc.