Posting here because my setup is pretty similar. Except I started with a fresh Krypton image. It is not possible to connect to a network with hidden SSID.
According to this guide it should be pretty straightforward. The problem is that the SSID is never being requested, connman and the GUI from within MyOSMC always prompt only for the password.
Connections are possible on visible networks.
Are there any known issues with RTL8191S WLAN adapters?