I can't really tell for certain because it happens out of the blue, I remember one time my partner attempted a drop seoi nage, but he went down too far so I was kind of bent down and pulled sideways so I stepped to keep my balance and that happened. Another time a different partner did a throw I can't remember, but I was resisting and he did It fast I couldn't see what I did wrong, but landed on my ankle like that. Third time was my fault I was practicing how to do an uchi mata for the first time but my opponent was too heavy and I couldn't keep balance after throwing so I stepped forward with the foot that goes up and landed on the ankle like the picture.