How do I get my custom Pulsar app to work after a Sandbox refresh?

When you refresh your Sandbox environment, you must take a few extra steps to ensure your Pulsar custom app works properly.

Check your permissions. Ensure your custom app file is in the content library and your users can access the library folder.
Update the Pulsar Settings with the correct Document ID for your custom app in your sandbox. Even though you may have copied your Pulsar Settings file from your Production environment, the document IDs for any referenced files have changed in your new Sandbox. This includes the document ID for your custom Pulsar app and any other files you may reference, such as HTML files. Refer to How do I find my Content Document ID for the steps to find the document ID for your custom Pulsar app.

Pulsar for Salesforce - Documentation