Testing plugin on dedicated instance

I’m trying to develop a plugin for my application, but am having trouble testing it. If I add it to my app, include the name of my app as the “App to test this plugin”, and include one of the actions in a workflow I get the debugger message:
General Error: The plugin null is in test mode and the current app is not the registered test app.

If I step through the workflow in the debugger it does not run my code and says [missing: 1539026727353x254486959372369920_current-AAC].

This error only happens on my main app - which is currently running as a dedicated instance. I’m wondering if this has something to do with it, because if I create a new regular app and use this instead, then the plugin runs correctly.