Really weird cause we literally had the same issue with our previous Brackeys game Descent. The shape of the main character was a square and we changed it to a circle and that helped. Eventually, we stopped using unitys rigid body, even though we still make our games in unity. My friend and programmer (who sadly couldn't join us for this project) got so upset with issues like that he rewrote completely the entire physics engine to suit better pixel art platformers we usually make.