Is the app freezing or crashing on your phone? Because of the smartphone variety, it's still not possible to test the app on every device before publishing it.
Please do some general steps at first:
If this doesn't help, please contact the developer via support@jurihock.de in English, German or Russian and describe how to reproduce the failure. The developer will contact you back as soon as possible and will try to help you.
If you're interested in further development of this open source hobby project, so actively help to improve it. Just giving a bad rating is useless!