Default changeset implementation allows only one operation

My OData service is exposed via a Gateway project by referring CDS models. At the beginning, everything works as expected until one day I received this error message after some adjustments to the service. Per ST22 data, the code triggers the exception as below.

The changes have been made was adding a DPC entity to the Gateway project, which means in the project, CDS models co-exist with DPC entity. Then I checked the same method of /IWBEP/IF_MGW_APPL_SRV_RUNTIME~CHANGESET_BEGIN in pure CDS derived service, as below.

Obviously, SADL takes over this for pure CDS scenario.

How to fix this:
1: If you are free to change your UI5 code, then it is easy to overcome this by adding parameter changeSetId during OData model calls.

2: Redefine method of /IWBEP/IF_MGW_APPL_SRV_RUNTIME~CHANGESET_BEGIN