After analysis, the cause of
this error was identified and corrected (the test play is still crashing but it is a different issue)
General Cause:
An old version of the project was deployed into its
own folder.
This caused the deployment files (such as the 'www' and 'locales' folders) to be mixed with the project files.
Specific Cause:
The package.json file was overwritten by the deployment and pointed to the wrong files to execute in a test play.
package.json
package.json can be thought of as a configuration file for the Node.js ecosystem. RPG Maker MV uses the NW.js framework which combines Node.js and the Chromium engine to deploy the game.
The package.json in the project folder identifies the file to execute for test play (normally it is 'index.html'). But, when a game is deployed, it points to a slightly different location ('www/index.html'). This caused the wrong html file to be executed in the test play, and this is a chain-reaction
[wrong html file is executed --> wrong plugins.js file is read --> it tries to load plugins that don't exist]
Fix:
The project is still a work in progress, so the deployment shouldn't have happened. The fix was to remove the files created by the deployment and correct the package.json file.