When plugins cause an error, any changes made during that edit operation are rolled back. Plugin actions are atomic – failure will revert the entire operation. That may be why you're not seeing any changes.

Debugging plugins

You can use the XD Developer Console to check for errors and debug. The Developer Console is in the app menu at:

Plugins > Development > Developer Console

Reloading development plugins

If you make any edits to your code, be sure to reload all plugins in the develop folder:

Plugins > Development > Reload Plugins

There's a tutorial in the XD plugin API docs with tips on debugging plugins.