in serverclass.conf for this client (or perhaps that is the default for this client). So when the client downloads the app, it doesn't restart splunkd. Therefore, the new app/configs do not take effect. You might want to change that.
You might not have needed to turn on debug. If you had searched the _internal index, you would probably have found much the same thing. Or at least you would have been able to see that the app was being deployed. I like to use a search like this:
index=_internal deployedapplication OR serverclass OR packagedownloadresthandler sourcetype=splunkd
| table _time host component log_level message
To test that this was the only problem, go to the client and see if the app appears. If yes, then restart splunkd. If that fixes the problem, then this was it!