Failed to parse mapping - NC15 with "Fulltextsearch - Elasticsearch"

Running 'sudo -u www-data php ./occ fulltextsearch:index' ends up in mapping error for _doc with my NC 15.0.7 and elasticsearch 7.0.
Similar posts found by google don't give me any hint how to solve it...

In Connection.php line 615: { "error": { "root_cause": [{ "type": "mapper_parsing_exception", "reason": "Root mapping definition has unsupported parameters: [standard : {dynamic=true, properties={owner={type=keyword}, groups={type=keyword}, circles={type=keyword}, metatags={type=keyword}, source={type=keyword}, title={copy_to=combined, analyzer=keyword, term_vector=yes, type=text}, content={copy_to=combined, analyzer=analyzer, term_vector=yes, type=text}, users={type=keyword}, tags={type=keyword}, provider={type=keyword}, subtags={type=keyword}, links={type=keyword}, combined={analyzer=analyzer, term_vector=yes, type=text}, hash={type=keyword}}}]" } ], "type": "mapper_parsing_exception", "reason": "Failed to parse mapping [_doc]: Root mapping definition has unsupported parameters: [standard : {dynamic=true, properties={owner={type=keyword}, groups={type=keyword}, circles={type=keyword}, metatags={type=keyword}, source={type=keyword}, title={copy_to=combined, analyzer=keyword, term_vector=yes, type=text}, content={copy_to=combined, analyzer=analyzer, term_vector=yes, type=text}, users={type=keyword}, tags={type=keyword}, provider={type=keyword}, subtags={type=keyword}, links={type=keyword}, combined={analyzer=analyzer, term_vector=yes, type=text}, hash={type=keyword}}}]", "caused_by": { "type": "mapper_parsing_exception", "reason": "Root mapping definition has unsupported parameters: [standard : {dynamic=true, properties={owner={type=keyword}, groups={type=keyword}, circles={type=keyword}, metatags={type=keyword}, source={type=keyword}, title={copy_to=combined, analyzer=keyword, term_vector=yes, type=text}, content={copy_to=combined, analyzer=analyzer, term_vector=yes, type=text}, users={type=keyword}, tags={type=keyword}, provider={type=keyword}, subtags={type=keyword}, links={type=keyword}, combined={analyzer=analyzer, term_vector=yes, type=text}, hash={type=keyword}}}]" } }, "status": 400 }

@daita Who can move this issue to nextcloud/fulltextsearch_elasticsearch/issues?

Originally posted by @af9 in https://github.com/nextcloud/univention-app/issues/70#issuecomment-484514273

Start by reproducing the reported sudo -u www-data php ./occ fulltextsearch:index failure with Nextcloud 15.0.7 and Elasticsearch 7.0. Inspect the fulltext search Elasticsearch integration and the _doc mapping shown in the error. Done means identifying why the mapping is rejected and documenting or implementing a confirmed resolution.