SELECT on views with join and/or union is not supported

Hello CAP Community,

I'm in the upgrade process from CDS 5.4 (Release August 2021) to CDS 5.6 (Release November 2021). That worked fine until I've made a request to an action that does a SELECT on a View that contains a JOIN. In 5.4 that worked just fine. Now with 5.6.4 it fails. This is the error log:

Error: SELECT on views with join and/or union is not supported
    at module.exports (/node_modules/@sap/cds/libx/_runtime/common/error/index.js:6:24)
    at _checkForForbiddenViews (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:486:13)
    at _getTransitionData (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:502:32)
    at getTransition (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:545:50)
    at /node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:567:16
    at Array.map (<anonymous>)
    at _entityTransitionsForTarget (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:560:19)
    at _newQuery (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:598:23)
    at resolveView (/node_modules/@sap/cds/libx/_runtime/common/utils/resolveView.js:616:20)
    at ApplicationService.handle (/node_modules/@sap/cds/libx/_runtime/cds-services/services/Service.js:131:17) {

The function that is called there is called _checkForForbiddenView.

Looking forward for your input how we can resolve this issue. I've checked the changelogs but I haven't found any indication in this direction.

CU
Gregor