I think the point you are missing here is that the person would be purposely altering the state of the device after it entered police custody, with the explicit intention of restricting access to the information that the device either 1) had directly, 2) had stored in cache, or 3) had access to through cookies, logins, etc.
If you are doing something to alter the device itself in any way (i.e. the bits anywhere on the device), it's a pretty straightforward path to the clink.
What isn't clear, though, is if the device was, for example, an "approved" device on some site/services and you logged into your accounts and removed access. Let's say for the sake of argument you had an encrypted chat app on your phone and that service has both web and mobile access. Your phone and laptop are approved devices. The police confiscate your phone. As soon as they release you, you log into your account from your laptop and remove the phone's access. The phone itself hasn't been changed. I wonder what would happen there.