m4v3rick
It seems the issue is resolved.
For the past four years, we've been using the local adapter, but I recently discovered that before that, Imgur was in use. When checking the settings, I noticed that the Imgur ID field was empty, likely due to a recent update. Although we no longer use the Imgur adapter, it was still required for older posts, which were marked in red due to an error.
However, the issue wasn’t limited to those marked posts—the entire discussion list on the main page was missing, even though no visible posts relied on the Imgur adapter.
In any case, re-entering the Imgur ID resolved the problem.