Bug: Columns show Content missing in public link view. Card view opens 404 error.

[david-uhlig]

When a board is accessed via its public link, certain columns display a "Content missing" message directly below their column name instead of showing their content. Additionally, clicking on any card opens a 404 error instead of the card's detail view.

This issue appears to be triggered by regenerating the public link. It does not occur the first time a public link is created, but consistently reproduces from the second generation onward.