The project was created as a CodenameOne project and just the sources were copied into it. Those files you say are in the project.
But for one class file the generated code warning (at the end of the file) was not created, this means CodenameOne plugin was already off at that time. I put a method that the class needed copying it from a similar class (initGuiBuilderComponents).
I performed all possible reset procedures, JDK change, close/restart, plugin uninstall/reinstall/disable/enable. Originally I downloaded the plugin and set to its path, but then it did not work as expected so I install from the IDE plugin store. No issue about the installation.
Regards