Hmm... This is certainly weird. I do wonder if it's a specific issue with the version that the tool uses by default. To test this out:
Download v0.53.1 of nwjs (the sdk version) from here: https://dl.nwjs.io/v0.53.1/
Then open a command line, cd to the nwjs folder (after unpacking) and run nw.exe --nwapp="<path to the game>" (Replace the <> with the actual path). If it also happens with that, then it's very likely that there's a compatibility issue with nwjs.