Since you said that you've tried with another Iphone and it did work maybe you should try to find an answer via Apple…?
I mean look a it this way, Eventide can't be responsible to fix the bugs from every single other manufacturers that is making some product that you're somehow using with the H9.
There's a lot of problem related to bluetooth and none of them are directly caused by the H9, but always because of some hardware or software bugs in another product…
(No, I don't work for Eventide but would rather have them working on new features for their own products than fixing someone else bugs)
Just my 0.02$