I have a couple of cards that are not on display on my board. When I search them they are showing as

[Andrea Cowley]

I have a couple of cards that are not on display on my board. When I search them they are showing as being there but I don't appear to be able to see them. 

[Олександр Новіцький]

I’ve run into this situation as well, especially when opening a board link from another team member. The issue was with the filters applied to the board. Press "F" and clear all filters. You will then see all the cards on the board.

[Ugnius Aušra]

Hey @Andrea Cowley 

I would suggest to check if board has no filters active right now. Maybe under filter conditions some cards can't be displayed.

Other i would thing of, that cards may be archived. Go to Menu → Archived items → Cards and check if they are there. If they are archived, you can send them back to the board.

Reference - https://support.atlassian.com/trello/docs/filtering-for-cards-on-a-board/