This is a known bug that will be fixed in the next release. It is caused by incorrect behavior after you have deleted the wallet seed.
Before the next release, you can reinstall the app (you will lose all testbytes) but don't try delete the seed in the current version.
This apps nothing backup fiture?
How do I restore the wallet if the device is damaged?
Since private payments are stored only on your device(s), and updated every time you send or receive blackbytes, the best way to protect from device failure is to have a multisig wallet with redundancy, e.g. 1-of-2 is enough for backup.
