I just tested r221 and NW 0.13.0 beta 5. Exported NWJs, same issue, black screen hang.
Going to remove GreenWorks and test.
ps. I've been using r218 with 0.13.0 alpha 7, as it's released on Steam. It works great but no Achievements.
Edit: Removed GW and tested, runs ok, saves are fine (I use a custom save system, using NWjs file read & write with JSON format arrays). But on exit (Browser Close), the nw.exe process won't close properly, remaining active. Prevents subsequent game launches.
0.13.0 beta 5 is non-usable in this state!
Bloody NWjs/Chromium, a step forward, a step back.