I've tracked down the root cause: I needed to disable two uBlock Filters in order to successfully load the page: Fanboy's Annoyance and Fanboy's Social. It seems that they block some JS related to social buttons (https://japan-dev.com/assets/socialButton.9ddbb1cc.js) and that makes the rest of JS responsible for the rest of the page to not execute (due to a failed request).
Sorry for the false flag.