Closed cards vanished from the boards

It does that for the first column and last column, to enable the board loadtime to be reasonable.
(Those columns may typically contain humungous amounts of cards, over time). You might have missed it (many people don't notice), but there's a "Show more items" link after the last card. Click that, and you can keep retrieving the next set of cards.

Myself, when there's something we're looking for which is Closed we're more likely to use Search or Query.