Answer
This points to the custom package's own metadata (the header/module-registration comment IFS's dictionary system relies on to recognize the package) conflicting with or not properly referencing itself — a projection can compile fine on its own but fail once a custom action tied to a package with mismatched metadata is added, since the underlying dictionary/projection-compilation logic depends on that metadata resolving cleanly. Review the custom package's metadata comment carefully for conflicts with how it's registered before assuming the projection action's own syntax is the problem.