It looks like, on the 12th of July, header HTML was changed from
<h1> tags to
<h1 id="..."> tag. Unfortunately, this broke at least one bot, as well as a userscript. This also has the potentially to do much more damage across the network via the various "auxiliary" features (userscripts, chatbots, automated scripts etc.) used by many members. Additionally, this will break any SEDE queries that search for
<h1> in the
Body field of the
Posts table. Finally, this may have introduced a bug with list elements as well as another bug.
I have no problem with Stack Exchange updating their HTML (presumably to improve the platform). However, a lot of users use systems such as userscripts to improve quality of life on sites and with specific features (reviewing, chat, etc.). It'd be nice if, for significant changes like this, we were provided some notice of the changes, so that we could fix our systems before they broke, not after, whether that be through an MSE announcement, or some other way that the team finds better. This helps ensure that the site's content curation isn't impeded in the meantime between the HTML change and when the script author gets around to updating it.