Just as a matter of interest, the method you describe to root worked fine eventually, with one hiccup.
The provisos for me were:- Install 'SuperSU 'BEFORE you install 'Disable Dm Verify.'
For some reason Dm verify would not install by itself first, the screen actually said "error cannot find SU", so I twigged that I had to install that first..
I installed the wrong version of Disable Dm, but it wasn't a big problem... the tablet "bricked" for about 10 mins and then I rebooted into recovery, downloaded an alternative version of Disable Dm, copied it to sd card and ran TWRP again and flashed the different version and bingo.
The best advice is "DON'T PANIC".
I was sure I had lost everything when it locked out for ages, but the HI10 pro seems to be fond of sulking, if you ignore it for 10 mins it comes round..lol.