If the title of the topic happens to have brackets in it, the hovercard skips over it. This is a problem for articles like en: Birdman or (The Unexpected Virtue of Ignorance) where the hovercard shows "Birdman or, often referred to simply as Birdman". I suggest to include the brackets when they are being bolded in the lead paragraph.
Topic on Talk:Page Previews/Flow
The concern with bracket content is that some articles have such long parenthesis with IPA keys etc that the preview content in the hovercard becomes useless.
Therefore, there's a need for better filtering of parenthetical ("bracketed") content. The current situation is clearly throwing out the baby with the bathwater. IPA templates, for example, create a span element with class="IPA"), so there are clearly identifiers that would let Hovercards be more specific in its content filtering.
Now filed as phab:T91344 . Thanks. Please edit or add details, there.
I came here about brackets, too. Hovercards are great while doing maintenance, to know what's the link about. However, most of the relevant information is in brackets (for example, date of birth). If bracketed content can't be filtered intelligently, preferences should allow users to select seeing or not seeing bracketed content.