Creating a new version of the DataTable from scratch after moving to 5.0 had the same issue.
FMyStruct is a c++ struct and is defined in a game plug-in. The plug-in’s module is in PublicDependencyModuleNames. The plugin is cooking and runs fine in the cook build. And I have a version of the code that bypasses the Datatable and that version has now problem with FMyStruct directly. It’s just the cook datatable.
I haven’t had time to try and reproduce just cooking a plug-in based TableRowBase in a project that relies on it.