Interesting! So you are getting data back from the /v1/instrumentation/content/visits endpoint, and you just cannot find that content_guid in the responses?
If people have viewed the application, it definitely should have data there! Are you a publisher / collaborator on the content, or an admin? If you are not a collaborator, then you will not have access to see the data about the application unless you are an admin.
Related, have you seen this report? It could show some patterns to follow for retrieving data.