I’ve been having the same issue with my iPad for a month now.  I realized the iPad must be the issure because my iPod allows both of my H9’s with no issues.  The Apple Store did a complete system restore on my iPad, but I still can’t get both pedals to stay connected.  At one time I could hit the two connect buttons really quick and get them to stay on, but not anymore.  It looks like I’ll be investing in a new 2017 iPad soon.