Search returns no results

For a reason I can't figure out fulltextsearch has stopped working and doesn't return any results whatsoever in Nextcloud. This applies to files and deck. After the latest update and the required upgrade to Elasticsearch 8 I had to reindex everything, after that everything worked fine.

Nextcoud v27.1.3
Full text search: 27.0.2
Full text search Elastisearch Platform: 27.0.4
Full text search files: 27.0.1
Full text search Files Tesseract OCR: 27.0.0

elasticsearch:amd64/stable 8.11.1

Elasticsearch is running, occ fulltextsearch:test says all ok, nc logs show no error:
Info | fulltextsearch_elasticsearch | Response time in 0.010 sec
Info | fulltextsearch_elasticsearch | Response (retry 0): 200
Info | fulltextsearch_elasticsearch | Request: POST http://127.0.0.1:9200/index/_search?from=0&size=5&_source_excludes=content

Any idea how to debug or what could be wrong?

Begin with the reported occ fulltextsearch:test result and the Elasticsearch 8.11.1 request shown in the logs; compare that successful response with an actual file or Deck search. No source file or failing test is named, so trace the full-text search entry point and reproduce the post-reindex failure. Done means identifying the cause and confirming that file and Deck searches return results again.