If you are currently reading a topic but also have chat opened to the side, each time you hover over a chat message or otherwise bring chat into focus with your mouse cursor the topic will scroll down a little bit. It will keep doing this until you reach the bottom. This is only an issue if you’re reading a topic. It has no effect if you are browsing a category. Also, this won’t happen if you are at the very top of a topic. If you scroll down a little bit on the topic, roughly until you get to the bottom of the first post, then this scrolling behavior with chat presents itself.
This is on an M1 Mac using Chrome.