G J shortcut does not reliably work after G N

When a Discourse installation produces this

on switching to a site and the shortcut G N is used a list of new topics is displayed. But the shortcut G J does not work. The shortcut X R does. The G J shortcut only becomes active by using G U then immediately G N. Seen this on numerous installs including here on Meta Discource but happens on all 17 Discourse installs where I am a registered/logged-in user.