Debugging with Android Studio stuck at "Waiting For Debugger" forever

Obviously is yet another Android Studio, or rather ADB bug.

Just use this command to disable it. adb shell am clear-debug-app

OR

Ensure there is nothing to wait for, by automatic uninstall from Device before each test-run, using Gradle's uninstallAll task, as mentioned in:
stackoverflow.com/Auto uninstall before install?

Restarting Testing device fix the issue for me.

On some machines/projects the debugger do not attach automatically so you need to attach it manually (studio menu -> Run -> Attach debugger to Android process)

Restarting Android Studio fix the issue for me.