https://ticket.wikimedia.org/otrs/index.pl?Action=AgentTicketZoom;TicketID=11401152
Original email in German, but I think they are trying to say that the article reader shouldn't allow horizontal scrolling, as present in the movie they attached. I have not personally tried to repro this yet.
Device Info: WikipediaApp/6.6.0.1742 (iOS 13.5; Tablet)