To reproduce this issue:
1. Setup DS 6.5.3 with idm-repo profile
2. Setup IDM 220.127.116.11, using DS node from step 1 as external repo
3. Adding the "city" property per https://backstage.forgerock.com/docs/idm/6.5/integrators-guide/#ds-repo-indexing
The indexed properties are listed in the array of fields for that managed object. To index additional managed user properties, add the property names to this array of fields.
4. REST GET /openidm/managed/user?_queryFilter=city+eq+'SG' would send to DS an ldap search with filter "(fr-idm-managed-user-json:caseIgnoreJsonQueryMatchManagedUser:=/city eq \"SG\")"
5. Debugsearchindex shows the search is unindexed.
In comparison, query on userName is indexed.