We have a user (on Skeptics.SE) with a long display name and no spaces (30 characters of Unicode). [I've chosen not to link to them; they are innocent here.]
There have have been several complaints that when that user leaves a comment it breaks the page layout.
I see no problems on my desktop (Chrome), but when I view it on my phone (Samsung Internet Browser), the display name appears in its full glory, and all the comments on that answer wrap at the same point as the last character - i.e. the comments overrun the column.
Update: as a temporary fix, I replaced one of the characters with a space. It didn't change the formatting problem - it didn't break at the space.