My ADB stopped working recently. All commands results in error: protocol fault (no status).
Follow trace.
adb devices
system/core/adb/adb.c::main
I had the same issue and found the problem: Android Studio.
Open the Android Studio menu Tools -> Android and uncheck Enable ADB integration.
Tools
Android
Enable ADB integration
adb devices should work (you might need adb kill-server first).
adb kill-server
Then you can re-enable ADB integration in Studio.