The set that is shown contains data for multiple entity types

What causes this issue?

There is data for several entity types in the set displayed. It has been
defined in your UI model, however, that single field selection is to be
carried out, meaning data for only one entity type.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

To fix the data inconsistency, delete the data for all entity types
except one.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.