After some detective work by @barbarabeeton it turned out the problem is not the display of downvote/deleted ads but that old ads from the last year get displayed.
Can the ads please be switched over to this years ads?
Please don't show community ads which have been downvoted and deleted during the voting phase.
For example this ad for an outdated event is currently displayed on tex.se
The corresponding meta post has been downvoted and deleted during the voting phase: https://tex.meta.stackexchange.com/a/8806/36296
Why is it nevertheless shown on the site? The announcement post said:
[...] they must have a minimum score of 6 at the time the post was closed/locked for submissions.