I did experience the same issue as nostr:npub1gzuushllat7pet0ccv9yuhygvc8ldeyhrgxuwg744dn5khnpk3gs3ea5ds though. if I didn't have the app installed from the playstore and attempted to install 0xChat from the APK it would fail to sign in. If I first installed from the playstore and updated with the APK then it worked.

also confirmed the latest version of Amber was installed <1.0.2>