This is my solution for our problem with safe Note v3 in iOS11.
1. Download iPhone BackUP extractor (demo version);
2. Select the BackUp containing your SafeNote (the last working backUp for me, created before updating to iOS 11);
3. When iPhoneBackUP extractor terminates the scan, Select SafeNote in the list of APP present in your BackUP;
4. The number of file and Database recorded in Safe Note will be displayed (see figure attached);

5. Select "All databases: Extract 1" (the free version of "iPhone BackUP extractor" allow you to extract limited number of files. We need the only one I indicated)
6. The "iPhone BackUP extractor" will save the following file (for example on your desktop): "\library\ProvateDocuments\CoreDataNotes.sqlite"
7. You can open this file with TextEdit and you can browse it in order to recover your password, otherwise you can download the software (freeware) "DB Browser for SQLite" [Releases · sqlitebrowser/sqlitebrowser · GitHub] and Browse data fo database and export every note saved in Safe Note in a natty way.
I hope this helps everything have my same problem.
EmuX