We released version 1.6.7. I can support iOS11 and fixed backup/restore function with Dropbox and Google Drive. If Dropbox authentication is failed and show white screen, please try to install original Dropbox application.
10/14/2017 Cloud NET, Inc. Support Team
Before iOS 11 version up, PLEASE update Wonder Notes to 1.6.4 later. If you run old version(previous 1.6.3) of Wonder Notes under iOS11, your input data will be deleted entirely! So, please backup your data to Google Drive or Dropbox in this time (Gear icon shows setting menu and select database backup and restore menu).
10/1/2017 Cloud NET, Inc. Support Team