OMG this Thread saved my life i got a Galaxy S7 just yesterday and i wanted to upgrade to Naugat but i encountered that problem i literally started freaking out thank you soooooooooo much
It worked like a charm. I completely removed everything from my phone through TWRP (No Installed Level). I came to this point just to fix lagging and battery drainage after rooting my phone.
But finally following instructions at XDA I was able to flash a custom ROM (latest one from same region)