Unable to mount /data after multiple wiped
How did you reflash the OS? using TWRP or ODIN?

A simpler solution is to flash Stock Firmware for your device via ODIN &amp; then flash TWRP again. 

You might first want to try the solution suggested on this XDA Thread if you are comfortable with using Terminal 
https://forum.xda-developers.com/showthread.php?t=2683787 

Reflashing the Stock Firmware via ODIN will most likely fix this issue.