This is not a new issue. If at the top of the page this doesn’t happen as that ad is below calendar, new threads etc. However, if scrolled down, it appears on top. The solution, while not perfect, is to scroll up before clicking on notifications.
The exact cause is due to how our ad system is set up and not something that is easily solved AFAIK.
There also an ad-free experience for less than 14¢ a day.