[SugarCube 2.x] Add format hangs?

I'm attempting to load the lastest verison of SugarCube 2.x into the latest offline version of Twine 2, and after giving Twine the path

file:///Z:/SugarCube-2/format.js

it simply hangs and 'spins' forever. If I click the 'X' and refresh my list of formats I can see SugarCube 2.x on the list, with a broken image for its logo. I can create new stories with this format, but I'm worried that it's corrupt somehow...

Is anybody else experiencing this? Should I be doing something differently?