It seems a recent upgrade broke something in the Master Detail Hierarchy in the IDE. The generated code works fine, but the IDE displays an error message. I noticed that one of my screens which was fine is now displaying the error message, so I created a small test Radzen project from scratch and the same issue occurs. See video below. Thanks.
Thank you for the report. This is a regression caused by a recent design-time optimization. We will restore this functionality with the next Radzen release.