Search scroll returning no hits (possible bug in 6.2?)

Elastic Stack Elasticsearch
4

It seems related with this issue: No hit using scan/scroll with has_parent filter

However I'm using 6.2 API, shouldn't that be fixed?
...
SearchRequest searchRequest = new SearchRequest(CIPHER_INDEX)
.source((new SearchSourceBuilder()
.query(QueryBuilders.boolQuery().must(getMatchQuery(searchFor)))
.postFilter(JoinQueryBuilders.hasChildQuery(ElasticConstants.CHILD_JOIN_REL,
filterByProcessAndCluster(reportMetadata.target().process(), processes, allClusters),
ScoreMode.None)
.innerHit(new InnerHitBuilder()))
.explain(false)))
.types(CIPHER_TYPE)
.searchType(SearchType.QUERY_THEN_FETCH);
...
elasticClient.search(searchRequest);
...
elasticClient.searchScroll(new SearchScrollRequest(result.getScrollId()))
...