When I'm taking an inharmonicity reading in the pitch raise mode, I have difficulty getting a reading on C8—it often takes 20 or more strikes of the key for there to be enough of a sustained tone to get a reading—sometimes it never is able to capture it. In those cases I simply skip it and move on, but wonder what that does for accuracy. Conversely, if I've been lucky enough to get a reading of C8 at some point, getting a new measurement of it (say, after doing a large pitch raise), Pianoscope will immediately be able to read it. Odd.
It has been the same on 4 different devices (iPhone XS Max, iPhone XR, iPhone 15 ProMax, and iPad Air 2 with each software upgrade since inception).