App Attach with Remote App fails

I setup Notepad++ using App Attach in my WVD environment. If I login to a desktop session, it works flawlessly. However, it perpetually fails when launching from a Remote App. (Error in the screenshots) I was wondering if anyone else had done this successfully? (I've seen a few articles elsewhere which seem like it should.)

I kind of suspect that it is a timing issue, as if the registration script hasn't completed before the app launches. I tried to fix this by disabling the logon script delay and running logon scripts synchronously. It still behaves the same way after these changes, so perhaps I am on the wrong track.