Well, if (as PPs suggest) the risk for police is that it may compromise confidential investigations, that must be because there is a security issue of some type about how the app interacts with other information on the phone. Otherwise this wouldn’t be an issue.
Not being a police officer, I do not have information about investigations in my phone, but I do have personal & private information which matters to me. If this app isn’t ready for the police, or the necessary checks haven’t been done, it should not have been rolled out yet.