I've found that the "linked issues" field (the count) does not appear on an idea card when I turn on the filter on a board of ideas. I've tested adding/removing as well as showing/hiding but still no result. The only change is the height of the cards adjusts as if the UI is making room for the element to be shown but it does not appear within the card.
Other fields like "created" and "comments" do appear on the cards when I add them to the board.
I've reported this to Atlassian and they think it's a bug. Just wanted to share here in case anyone else notices this behavior.
Thanks!
Matt