I believe your issue is due to a Magisk remnant in your /data folder. look for a file with the extension .sh and delete it. SuperSu should then flash and boot up just fine.
Sent from my Pixel C using Tapatalk
Dude, I can't thank you enoug...
cant really help you, but i may be able to offer some info.
im guessing you are either running Marshmallow, or have a nexus running stock?
if no, then the rest may be irrelevant.
i believe it was in M, google implemented some sort of system wr...
All good here Lucky you. So this seems like a problem with my phone, but I can figure out why.