When the chat contains event placed across multiple days, a logarithmic scale time categories list is displayed. It works great in wide mode, but hide parts of the message (and it laggy) in non-wide mode. It is also very useful to help locate messages. But is (pretty) visual noise when you are not trying to locate some messages. In wide mode, it falls in the, "what the hell, there's plenty of room and it's pretty" category, but on mobile it's annoying. To fix this, I plan to add a special mode where this thing is only displayed when you press on a special mobile scrollbar handle.
It was removed from the mobile layout for now.