I stopped debugging the Debugger itself, and I started enjoying to debug why the app crashes (syscall fails abnormally) when it spawns new thread in the spawned thread function, for now.
But after I frustrated enough to wait minutes per debug session, probably I will be back to debug the Debugger again… 
When debugging the Debugger I noticed it takes long to load .debug_info section
(maybe it is the meat of the DWARF), and to notify UI that debug info loaded that I guess there is the place the Debugger Kit passes loaded enormous data to the UI.
Maybe loading .debug_info partially for example in LRU algorithm is easier but the communication between the kit and the app looks harder. Probably some refactoring will be needed.