Prepare All Plugin Modules For Deployment does no add module classes

I have an existing plugin that I am attempting to upgrade for IDEA 2019.3.

The plug-in works fine in debug mode, however, when I run the ‘Prepare All Plugin Modules For Deployment’, the generated zip file is missing the some class files. The core plugin classes are missing as well as classes from 3 of the 4 imported modules. The dependent jars for the imported modules as well as the resources are included in the zip file.

I have spent the day trying different options in the Modules section of the Project Structure dialog, as well and rebooting, cleaning cache, and even creating a brand new plugin project with the existing source, to no avail.

Any help would be appreciated.

Thanks,

Don