I have noticed the problem also, and sent some screenshots of it to WGTNico in Discord on 1/25. He replied that they found another similar issue with weird magnification and he's 99% sure it's related to that. He said he would add the large chat font issue to the ticket.
FWIW, I noticed the large chat font issue is there when you play in 1920x1080 fullscreen. But if you play in 1024x768 fullscreen, the chat font is normal size.