- the outside rein is too long with no contact
- the inside rein is too short and stiff
Therefore the stride is shorter on the inside.
To correct, ride shoulder-in. This helps to improve the correct lateral bending and encourages the horse to take a contact with the bit on the outside. And it encourages the inside hind leg to engage well forwards.
Sometimes this fault is easier to correct by interrupting shoulder-in, riding a volte, and then proceeding with a new shoulder-in.