After upgrading to Android version 6.0 Bluetooth Low Energy (BLE) scanning will only work if Location services are enabled on the device. See here for reference: Bluetooth L
I also tried this on manifest but did not request permission, not sure why. Is you app prompting for Location permission on startup? If it's not, we need to request for permission on runtime.
Also you can check this to test if your app is working fine:
Open Settings > Apps > YourApplication > Permissions and enable Location and then try to scan for results.
Location will be listed here only if you have provided ACCESS_COARSE_LOCATION on manifest.