The ad in the side menu sometimes is the same size of the top banner ad (in that case, 729px x 90px). I managed to reproduce this a few times on the Home page and on the question page.
Browser 1: Opera GX - version LVL2 (core: 76.0.4017.208)
Browser 2: Chrome - version 91.0.4472.124
OS: Windows 10 - version 2004 (OS build 19041.1083)