In my case it was a combination of:
1. Install SuperSU only on /data, not on /system - there's an option for that in SuperSU
2. Uncheck "Enable Superuser" in SuperSU settings
3. Reboot device
Not directly related to this subject, but I find I always have to recalibrate the gyro after every reboot. Happens on both my S5 and my older S4.
Pry-fi is broken. I had similar issues after using it. Check my reply & fix in the pry-fi thread: http://forum.xda-developers.com/showpost.php?p=55449565&postcount=405
For better ping values you need to disable wifi optimisation.
Chainfire: is there any way to hide the su binary and SuperSU app from peeking apps like DME that refuse to launch if the phone is rooted?
Actually, unchecking "Enable Superuser" from the settings does exactly that. Unfortunately, the app also c...