Everything else about the game works flawlessly on Windows 10.
Steps to reproduce the issue:
- Launch the game launcher, input your Square Enix ID, password, one time password
- Make sure to check Remember Square Enix ID check box.
- Successfully launch the game and start playing
- Exit the game
- Restart the launcher, Sqaure Enix ID has been forgotten
Issue reproduced with two machine upgraded from Windows 8.1 to Windows 10.