Solver results in status 4

Greeting acados community, :wave:

I am trying to run a simple MPC scheme on an inverted pendulum and I noticed there is a miscalculation of my cart velocity by the solver. In reality the cart jams, i.e., velocity is zero but the OCP calculates a non-zero cart velocity. On further investigation I noticed that the solver returns status 4 one step before the velocity deviates from the real thing and continues to return status 4 for a few 100 steps. This happened too many times for it to be a coincidence.

My question is this: Does status 4 mean that the solver couldn’t find a solution? If so, is that an feasibility issue or a solver parameter issue? Is there any way to find out? Just for reference, I am using SQP with RTI for solving the OCP.

Thank you in advance :pray: