Looks like DevTools has some problem in JS code.
It is a chance that problem will be solved by chrome restart. Usually that happens when chrome is upgrading at background.
The other reason of that can be some changes which you have made in DevTools.js.
Of cause if you do some changes
You can troubleshoot such problem by another instance of DevTools.
As example you can try to load DevTools.html page into Safari, open WebInspector for it and check console messages.