MONDO native-term filtering returns empty results and search hits have empty obo_id

[Paco-Danes]

Hi OLS team,

MONDO native-term filtering appears to be broken in the public OLS4 API and UI at the moment.

Observed on 2026-04-29 against www.ebi.ac.uk/ols4.

Reproduction

Legacy search endpoint:

https://www.ebi.ac.uk/ols4/api/search?q=cancer&ontology=mondo&local=true&rows=1

Current result:

response.numFound = 0

But the same query using imported=false returns MONDO hits:

https://www.ebi.ac.uk/ols4/api/search?q=cancer&ontology=mondo&imported=false&rows=1

Example current hit:

{
  "iri": "http://purl.obolibrary.org/obo/MONDO_0004992",
  "short_form": "MONDO_0004992",
  "label": "cancer",
  "obo_id": "",
  "is_defining_ontology": false
}

Similarly, v2:

https://www.ebi.ac.uk/ols4/api/v2/entities?search=cancer&ontologyId=mondo&isDefiningOntology=true&size=1

returns totalElements = 0, while:

https://www.ebi.ac.uk/ols4/api/v2/entities?search=cancer&ontologyId=mondo&imported=false&size=1

returns MONDO classes such as MONDO_0004992, but with:

{
  "ontologyId": "mondo",
  "iri": "http://purl.obolibrary.org/obo/MONDO_0004992",
  "label": ["cancer"],
  "imported": false,
  "isDefiningOntology": false
}

Expected

Native MONDO terms/classes should be returned by native-only filtering. For example, MONDO_0004992 should likely be treated as defining/native for the mondo ontology.

Also, for /api/search, obo_id appears to be empty even when short_form and iri clearly identify an OBO term such as MONDO_0004992. This breaks clients that rely on the legacy obo_id field.

Additional observation

The MONDO ontology metadata currently reports fallback status:

https://www.ebi.ac.uk/ols4/api/v2/ontologies/mondo

shows:

{
  "is_fallback": true,
  "fallback_reason": "Latest ontology version is failing to load, using the last successful version instead",
  "ontologyPurl": "https://purl.obolibrary.org/obo/mondo/mondo-international.owl"
}

So this may be related to the current MONDO ingest/fallback state rather than search ranking itself.

Thanks!

[haideriqbal]

copying my answer from other thread:

This must be a bug on our side, since we have rewritten our Solr implementation and the way it is indexed, so we probably introduced it. I'll be looking at both of these issues to see what's really happening.

[dglemos]

Hi, I'm also facing this issue.
The OLS4 API response is missing data https://www.ebi.ac.uk/ols4/api/search?q=MONDO:0100250&ontology=mondo&exact=1