This is currently a known issue. Sometimes this issue can be repaired by doing the following steps:
- Uninstall/Reinstalling the app
- On iOS, try first to log in via Apple ID. Then log back out. Then log in via Google.
- Check to make sure your Google account does not have any restrictions, such as if your Google Drive storage is over the storage limit.
- Check to make sure you are not transferring from Android to iOS/iOS to Android. If your email login is connected to a different platform, you may need to contact Support to unlink the email from your old account.
If none of the above steps fixes your issue and you have not yet contacted support, please submit a support ticket here.