Maybe the only way is to uninstall TE2015 from your mobile, find and install the old version, 2014 (but you can find it only for android, not for ios).
The best way would be if Nordeus fixed it Auto-assignment in mobile apps might be a feature - a stupid one, but still a feature -, but in the web version, where it sometimes is and sometimes isn't auto-assigned, it must be a bug, I think