I've been using Chainfire's SuperSU on quite a few devices for a while and it's really great, but on a Lenovo Tab 4 (TB-8504F) whenever I do a factory reset I lose root. I have rooted quite a lot of devices successfully through OEM bootloader unlock and flashing via TWRP. SuperSU is definitely in the system partition and the device doesn't have multiple slots.
I'd like to make root permanent but I'm really not sure how to go about this as from my understanding nothing in /data is required for the /system stuff to work for SuperSU
Any pointers would be great, thanks