Reported first on English Wikipedia all articles about zero (0) (where 0 is the actual title) are not showing the first title heading and it's empty in the HTML code.
Steps to produce
Go to English Wikipedia's article about "0" https://en.wikipedia.org/wiki/0
*Or to nn.wiki https://nn.wikipedia.org/wiki/0
*Or to this redirect on fr https://fr.wikipedia.org/w/index.php?title=0&redirect=no
The first heading of all pages above show 0
They show nothing. But may contain (editsection) link, I guess that's based on a user preference.
This happens only on Vector skin, all other skins display normally including mobile ones