We have an Oracle server hosting GIS data. All of our schemas are inside one instance in the database. One schema is called 'DEV'. In ArcCatalog we can't change its 'owner' to 'DEV' user (using the 'geodatabase connection properties' window): We get a 'Maximum Number of Connections to Instance' like error. The owner, by default, is always 'SDE' but that is wrong owner and so shows wrong features/tables. And we can change the owner to some other users but they would show wrong features.
What is interesting is that in the 'Oracle SQL Manager' client we could use the credentials for the DEV user and correctly see the Features/Tables. Our database person confirms that connections to the instance are indeed not maxed out.
So the issue is in ArcCatalog only. And the issue persists on ArcCatalog running on two different workstations.