Optimization reaches minimal step length

[mpt0816]

Hello！ I has a problem when solving an MPC problem. The Hpipm solver returns code 2, similar to issue #56. Strange to say, it would return code Sucess when removing the first general constraint. But, the MPC problem meet the first constraint. In addition, the MPC problem can be solved by OSQP. Switching to the robust mode and reducing the exit tolerances do not work.