Android - Soft bricked Moto G4 (XT1625) after SuperSU install
Proper research would have prevented this, in the future if you need information on rooting a device, go to a REPUTABLE source like XDA or a similar forum and make sure the information is specific to your device AND the current Android version. Lollipop, Marshmallow, and now Nougat are changing the way rooting is being done.
All retail/unlocked Moto devices running Marshmallow have an extra step that is required when flashing to force a systemless root installation by the SuperSU install script.
After successfully flashing TWRP and booting it, go to
Terminal and enter:
And press Enter, then exit. The spelling and spacing must be exact or it won't work. Then go to the main menu of TWRP and flash SuperSU normally, you should see the script specifically state it is doing a systemless install and patch the boot image (and in your case, cleanup an old standard root installation).
Please use only the referenced version from my thread (yes, I am the original author of that source thread), they are tested and working to both root the device, and cleanup a failed root.
Be aware on the first boot after this procedure, the device will boot loop twice, do not be concerned, this is normal, then it will boot normally after that.
And since you did not do a nandroid backup before rooting (shakes head), you may need to flash back to stock via fastboot before this procedure will work. The image for your device is available here. Remember that you cannot flash this in TWRP, you MUST flash each partition manually with fastboot and this will return the device to out of the box condition.