Replace feature class in a geodatabase

[PaoloGull_sow]

This post is related to https://community.esri.com/t5/data-management-questions/replace-existing-feature-class-data-with-new... but i want to pose a more specific question

Using ArcGIS 10.7.1 or ArcGIS Pro 2.3 I need to replace one feature class with another where the geometries are different but the structure is the same. No problem with the tools indicated in the previous posts BUT, when I go to use the feature class, the relationship classes no longer work. Also in this case the relations apparently remain valid but are not read. Why? I can't rebuild all relationships every time on every feature class update. Any suggestions? Thanks in advance

as you can see the relation is empty:

[Robert_LeClair]

My guess is when you replace the original FC with a new FC (changed geometries), something about the ObjectID of the FC and the Relationship Class properties gets changed therefore breaking the link.  Just a guess though.

[PaoloGull_sow]

Following your intuition I checked step-by-step all items involved in the relationship as follows

These are some records from the Relationship class and the related table. ID_ELEMENTO and ID (They are two arbitrarian and unique text fields) are the keys 

If I delete these records in the feature class the keys in the related table (ID) become empty

NOTE that the relation is set up as "simple" but the objects don't seem really independent

Is very annoying and strange at the same time