I have a Bluetooth LE module I connect to with an App (Xamarin based, but not sure that's important).
I have noticed that I have some case where I connect to the module, then quickly (attempt to) disconnect, and the module "disappears". It does not show on scans from other devices.
What's really surprising is that the module stays "invisible" until I turn off the android device I ran the app on, or power-cycle the device with the module. Surprising to me -- even turning off Bluetooth in android device does not "free it up", BUT "Airplane Mode" does!
I was able to verify that when it gets into this "invisible" mode, the module believes it is still connected. But I assume that the android Bluetooth stack should drop the connection when the app exits. And even if not, turning off Bluetooth would end connections, wouldn't it?