In my case, selecting Debug JS Remotely launched Chrome, but did not connect with the android device. Normally, the new Chrome tab/window would have the debugging URL pre-populated in the address bar, but in this case the address bar was blank. After the timeout period, the "Unable to connect with remote debugger" error message was displayed. I fixed this with the following procedure:
adb reverse tcp:8081 tcp:8081
http://localhost:8081/debugger-ui
into the address field of my Chrome browser. You should see the normal debugging screen but your app will still not be connected.That should fix the problem. If not, you may need to take the following additional steps:
react-native run-android