Update: I had a chat with a guest experience manager yesterday and she's spoken with the head of security who's briefed security about my device, ironically they tried it again yesterday but I simply refused to place it in the tray.
I had no issues with bag check today, they even protectively said "no need to worry about your iPad" (it's a galaxy tab a 10.1 2016...) and they confirmed by nodding when I said "so you got the memo"
Today the manager catches up with me when I was popping to reception to tell her it went ok, and then says she wanted to introduce me to the head of security.
so I had a chat with the guest experience manager, two members of security and the head of security, the head said I shouldn't have any issues and should just be able to walk through the arch with my device but might need to hold it in various positions so they can confirm what is alarming (lights on the side say where there alarming object is).
All in all I'm now fairly confident I won't have this issue again, at least not until FRIGHT NIGHTS and even then I can probably request a manager to pop down to bag search.