It doesn't work on androd 6.0. I tested on LG and HTC devices. I would like to use this on CM 13. I have downgrade my phones to cm 12.1 (android 5.1) so I can't send log.
I hope you can improve your app.
Many Android 6.0 users are using Boldbeast Recorder, paid or unpaid. The app works very well.
CM13: CM13 Call Recording