For me the issue was signing into my Google account on the debug Chrome window. This had been working fine for me until I signed in. Once I signed out of that instance of Chrome AND choose to delete all of my settings via the checkbox, the debugger worked fine again.
My non-debugging instance of Chrome was still signed into Google and unaffected. The main issue is that my lovely plugins are gone from the debug version, but at least I can step through client code again.