Release 1.16 fixes some autofocus problems that caused traps on some devices. If this version does not recognize diagrams then in settings uncheck the continuous video autofocus flag.
Release 1.15 allows recognition in both portrait and landscape mode, and deals correctly with orientation changes. If you don't want automatic screen rotation just disable it on the device, or follow the instructions above to reinstall ChessOcr 1.13 (which does not autorotate) and disable updating of the app.