Hello,
how are the relationships executed? With relationship classes or directly via Join/Relate in the MXD?
Because see here:
Author maps to publish feature services—Documentation | ArcGIS Enterprise
Feature services allow queries on related data, but only if the relationship is defined through a geodatabase relationship class. If a published map document has a layer and table related through a geodatabase relationship class, the feature service allows queries on the layer to return objects from the related table. Note that to support queries that return related objects, you must include the table and layer involved in the relationship class in the published map document. If either the origin or destination layer or table is not included in the map document, the feature service ignores the relationship.
Note:
For attributed relationship classes, also include the relationship class table in the map document.
Are the relationships displayed via the REST interface?
