Since updating to macOS Sierra 10.12.4, I’ve had problems accessing my Mac using screen sharing and VNC from my iPad. Using another Mac is fine, but authenticating using the iPad’s onscreen keyboard fails. Using a Bluetooth keyboard with the iPad works fine. What’s up?
This is a bizarre bug which appears to be confined to that version of Sierra, which means the on‑screen ß key doesn’t work on the iPad. If you enter a password containing capitals, Apple’s VNC server – to which the iPad is trying to connect – sees lowercase letters and rejects it.
As you’ve discovered, you can work around it by not using an iOS on-screen keyboard; a Bluetooth keyboard or a Mac will do nicely, though. You could also change your password so it doesn’t use capitals. The issue is independent of your choice of VNC app on iOS, and appears to occur somewhere between 10.12.4 and Apple’s VNC Server. If you substitute another VNC server, such as RealVNC ( realvnc.com), then the on-screen keyboard works normally again.
If macOS 10.12.4’s Screen Sharing feature no longer accepts your password from an iOS device, try eliminating capitals.