On Hinduism SE, the sidebar has a Hot Meta Post whose title contains a URL, and this URL overflows outside the edge of the sidebar.
The displayed title of the question is
Why is this question https://hinduism.stackexchange.com/q/40266/20829 marked... where the URL starts on a new line and extends beyond the edge of the sidebar.
I expect the same issue will come up whenever a very long word appears in a title.
It is known that the same error occurs in the chatroom sidebar if the name of a chatroom is very long: Long chatroom name overflows sidebar widget