https://api.listenbrainz.org/1/metadata/lookup/?recording_name=No+Time+to+Die&artist_name=Billie+Eilish&metadata=true returns performer rels (they have no dates)

https://api.listenbrainz.org/1/metadata/lookup/?recording_name=Bridge+Over+Troubled+Water&artist_name=Simon+%26+Garfunkel&metadata=true returns no performer rels (they have dates)

The main pattern which I could spot was that recordings where (all) relationships have date attributes do not seem to return rels. I haven't yet found a case where only some rels have dates to see if that would make the LB API return only those without.