Fixed the issue by replacing the contents of the nw directory, <purr data root>/lib/pd-l2ork/bin/nw which apparently contains the nw.js version from 05-2017, with the newest one I downloaded from https://nwjs.io/. Haven't used it much yet, but so far everything's looking great, and working without problems.

I'm using purr-data latest version Pd-l2ork-2.9.0 20190507-rev.22573662 on Ubuntu 18.04.2, and there's something wrong with fonts. As you can see in the screenshot below, many characters such as d, a, h, p have some reddish line on their borders. Any ideas on what's going on?