Seems like this H9 Control App – Mac OSX 10.8+ Version 3.5.4 update messed up everything as nothing works anymore. No bluetooth, no server connection…
I lost so much time with this thing not working, It's insane.
Hm, I'm sorry to hear that you're having so much trouble after installing the latest version. I just installed it myself on my iPhone, and connecting to my H9 and registering the H9 all worked without any issues. This latest release just had a small bug fix for a crash that could occur while working in the preset list screen. So, there shouldn't have been any code changes that would have caused these sorts of problems. What kind of device are you using with which OS version installed?
The H9 Control manual has a bunch of trouble shooting tips at the beginning of the manual. I don't know what you've tried already, but it has all the tried and true tips for dealing with connectivity problems: