Install Magisk on Samsung Galaxy S7 Edge (SM-G935FD) UAE ROM
Yep.
I finally solved my issue late last night. In recovery, using TWRP, after trying to install Magisk, I'd get a response that was something like "unable to mount /data partition"..and I believe that was what was causing the issue. I found this html site at XDA developers 

https://forum.xda-developers.com/android/general/how-to-fix-unable-to-mount-data-t3830897

which steps you through the process of repairing the data file systems (both ext2 and ext4), and that worked. Magisk installed correctly and is now working with my banking details, as well as Samsung Health (which involved changing a digit in the System/build prop file (tima from 1 to 0).

Now if someone could show me what to do when the next samsung update comes along, I'd be grateful. Don't want to lose it all (Magisk install) after the next update...