I tracked this down to malformed YAML front matter in a couple of your Markdown files. One of the description fields starts with a normal double quote but ends with a smart quote, so the front matter parser cannot read it.
Related Items made the issue visible because it scans the other items in the same collection to find matches, so a single malformed item can trigger the error even when viewing a different page.
We’ll tighten up the parser so it can recover from this specific quote mismatch, but correcting the front matter quotes in those Markdown files will also resolve the issue.
Affected content files I found:
- kochen-ist-leidenschaft.md (line 36)
- kochen-leicht-gemacht.md (line 39)
Both have description.short values that open with a normal quote " but close with a smart quote “, which makes the YAML front matter invalid.